"uuid","repository link","title","author","contributor","publication year","abstract","subject topic","language","publication type","publisher","isbn","issn","patent","patent status","bibliographic note","access restriction","embargo date","faculty","department","research group","programme","project","coordinates"
"uuid:afb15a01-05a0-4941-8c40-e194516209bd","http://resolver.tudelft.nl/uuid:afb15a01-05a0-4941-8c40-e194516209bd","Interparticle friction in sheared dense suspensions: Comparison of the viscous and frictional rheology descriptions","Peerbooms, W. (TU Delft Multi Phase Systems); Nadorp, Tim (Student TU Delft); van der Heijden, A.E.D.M. (TU Delft Complex Fluid Processing; TNO); Breugem, W.P. (TU Delft Multi Phase Systems)","","2024","In the literature, two different frameworks exist for describing the rheology of solid/liquid suspensions: (1) the “viscous” framework in terms of the relative suspension viscosity, ηr, as a function of the reduced solid volume fraction, f=fm, with fm the maximum flowable packing fraction, and (2) the “frictional” framework in terms of a macroscopic friction coefficient, μ, as a function of the viscous number, Iv, defined as the ratio of the viscous shear to the wall-normal particle stress. Our goal is to compare the two different frameworks, focusing on the effect of friction between particles. We have conducted a particle-resolved direct numerical simulation study of a dense non-Brownian suspension of neutrally buoyant spheres in slow plane Couette flow. We varied the bulk solid volume fraction from fb ¼ 0:1 to 0.6 and considered three different Coulomb friction coefficients: μc ¼ 0, 0.2, and 0.39. We find that ηr scales well with f=fm, with fm obtained from fitting the Maron–Pierce correlation. We also find that μ scales well with Iv. Furthermore, we find a monotonic relation between f=fm and Iv, which depends only weakly on μc. Since ηr ¼ μ=Iv, we thus find that the two frameworks are largely equivalent and that both account implicitly for Coulomb friction. However, we find that the normal particle stress differences, N1 and N2, when normalized with the total shear stress and plotted against either f=fm or Iv, remain explicitly dependent on μc in a manner that is not yet fully understood.","","en","journal article","","","","","","","","","","","Multi Phase Systems","","",""
"uuid:a31ccc22-b7c2-4190-a117-8392668f2a04","http://resolver.tudelft.nl/uuid:a31ccc22-b7c2-4190-a117-8392668f2a04","Role of turbulent kinetic energy modulation by particle–fluid interaction in sediment pick-up","Keetels, G.H. (TU Delft Offshore and Dredging Engineering); Chauchat, Julien (Université Grenoble Alpes); Breugem, W.P. (TU Delft Multi Phase Systems)","","2023","Reliable prediction of the erosion rate of sediment beds is important for many applications in coastal and river engineering. Theoretical understanding of empirically derived scaling relations is still lacking. This applies in particular for the scaling anomaly between low and high Shields number conditions. In this work, the erosion process is studied from the perspective of the phase-averaged turbulent kinetic energy (TKE) equations. The multi-phase TKE equations are written in a form that allows for a direct comparison with the TKE equation that appears for a stratified single-phase flow under the Boussinesq approximation. This reveals that next to buoyancy destruction, several other TKE modulation mechanisms become important at high Shields numbers and concentrations. Two scaling laws are derived for both moderate and high Shields numbers, and are tested against a wide range of experimental data.","sediment transport; particle/fluid flow; stratified turbulence","en","journal article","","","","","","","","","","","Offshore and Dredging Engineering","","",""
"uuid:fc0820da-9c4a-4f15-ba94-98c408a40a47","http://resolver.tudelft.nl/uuid:fc0820da-9c4a-4f15-ba94-98c408a40a47","Controlling the breakup of spiralling jets: results from experiments, nonlinear simulations and linear stability analysis","Kamis, Y.E. (TU Delft Multi Phase Systems); Prakash, Suriya (TU Delft Complex Fluid Processing); Breugem, W.P. (TU Delft Multi Phase Systems); Eral, H.B. (TU Delft Complex Fluid Processing)","","2023","We experimentally and numerically study the dynamics of a liquid jet issued from a rotating orifice, whose breakup is regulated by a vibrating piezo element. The helical trajectory of the spiralling jet yields fictitious forces varying along the jet whose longitudinal projections stretch and thin the jet, affecting the growth of perturbations. We show that by quantifying these fictitious forces, one can estimate the jet intact length and size distribution of drops formed at jet breakup. The presence of the locally varying fictitious forces may render high-frequency perturbations, that would otherwise be stable in the abscence of stretching, unstable, as observed similarly in the case of straight jets stretching under gravity. The perturbation amplitude then dictates how strong the perturbation is coupled to the jet compared with random noise that is inherently present in any experimental set-up. In the present study we exploit the slenderness of the jet to separate the calculation of the base flow and the growth of perturbations. The fictitious forces calculated from the base flow trajectory are then used in a nonlinear slender-jet model, which treats the spiralling jet as a quasi-straight jet with locally varying body forces. We show both experimentally and numerically that jet breakup characteristics (e.g. intact length and drop size distribution) can be controlled by finite-amplitude perturbations created by mechanically induced pressure modulations. Finally, we revisit the integrated net gain approach developed for straight jets under gravity and we provide simple analogous relations for spiralling jets.","instability control; nonlinear instability; breakup/coalescence","en","journal article","","","","","","","","","","","Multi Phase Systems","","",""
"uuid:8e94c716-34f1-4a41-a872-9c057fc979ec","http://resolver.tudelft.nl/uuid:8e94c716-34f1-4a41-a872-9c057fc979ec","From nearly homogeneous to core-peaking suspensions: Insight in suspension pipe flows using MRI and DNS","Hogendoorn, W.J. (TU Delft Complex Fluid Processing); Breugem, W.P. (TU Delft Multi Phase Systems); Frank, David (Universität Rostock); Bruschewski, Martin (Universität Rostock); Grundmann, Sven (Universität Rostock); Poelma, C. (TU Delft Process and Energy)","","2023","Magnetic resonance imaging (MRI) experiments have been performed in conjunction with direct numerical simulations (DNS) to study neutrally buoyant particle-laden pipe flows. The flows are characterized by the suspension liquid Reynolds number (Res), based on the bulk liquid velocity and suspension viscosity obtained from Eilers' correlation, the bulk solid volume fraction (φb), and the particle-to-pipe diameter ratio (d/D). Six different cases have been studied, each with a unique combination of Res and φ, while d/D is kept constant at 0.058. The selected cases ensure that the comparison is performed across different flow regimes, each exhibiting characteristic behavior. In general, an excellent agreement is found between experiment and simulation for the average liquid velocity and solid volume fraction profiles. Root-mean-square errors as low as 1.7% and 5.3% are found for the velocity and volume fraction profiles, respectively. This study presents accurate and quantitative velocity and volume fraction profiles of semidilute up to dense suspension flows using both experimental and numerical methods. Three different flow regimes are identified, based on the experimental and numerical solid volume fraction profiles. These profiles explain observations in the drag change. For low bulk solid volume fractions a drag increase (with respect to an equal Res single-phase case) is observed. For moderate volume fraction distributions the drag is found to decrease, due to particle accumulation at the pipe center. For high volume fractions the drag is found to decrease further. For solid volume fractions of 0.4 a drag reduction higher than 25% is found. This drag reduction is linked to the strong viscosity gradient in the radial direction, where the relatively low viscosity near the pipe wall acts as a lubrication layer between the pipe wall and the dense core.","","en","journal article","","","","","","","","","","Process and Energy","Complex Fluid Processing","","",""
"uuid:dca0c009-3109-49b2-9eed-e5694f27454d","http://resolver.tudelft.nl/uuid:dca0c009-3109-49b2-9eed-e5694f27454d","Inertial effects in sedimenting suspensions of solid spheres in a liquid","Shajahan, M.T. (TU Delft Multi Phase Systems); Breugem, W.P. (TU Delft Multi Phase Systems)","","2023","Particle-resolved Direct Numerical Simulations have been performed on the gravitational settling of mono-disperse solid spheres in a viscous fluid and triply periodic domain. In a comprehensive study, the bulk solid volume concentration was varied from ϕ=0.5 to 30%. To study the effect of inertia, three different Galileo numbers were considered in the inertial regime, Ga=144, 178 and 210, for which a single settling sphere exhibits distinctly different wake and path characteristics. The particle/fluid mass density ratio was fixed at 1.5. We find that for ϕ=2−30% the suspension microstructure and dynamics depend predominantly on the bulk concentration. In qualitative agreement with previous studies in literature, three different sedimentation regimes can be distinguished: (1) the dilute concentration regime for ϕ≲2% with preferential settling of particles in vertical trains, (2) the moderate concentration regime for 2%≲ϕ≲10% with preferential settling of particles in horizontal pairs with an interparticle distance of ∼ 1.5 particle diameters, and (3) the dense concentration regime for ϕ≳10% with a nearly random (“hard-sphere”) distribution of the particles in space. The clustering of particles is dictated by, respectively, trapping of particles in the wake of other particles, a drafting–kissing–tumbling (DKT) instability by which two vertically aligned particles quickly reorient themselves into a horizontally aligned particle pair, and short-range multiparticle interactions through viscous lubrication and to a lesser extent collisions between particles. In all cases, hindered settling at a reduced speed is observed as compared to a single settling sphere. The well-known Richardson–Zaki relation for the mean sedimentation velocity appears valid only for the dense concentration regime. We provide ample evidence that in the dense regime the characteristic velocity and time scales of particle motion are proportional to gDp and Dp/g, respectively, with g the gravitational acceleration and Dp the particle diameter. We also observe an ω−3 scaling of the particle velocity spectra for ωDp/g≳0.4 and we propose a model to explain this scaling behavior, based on the inertial response of the particles to small-scale flow perturbations. Kinematic waves, i.e., vertically propagating plane waves in the local concentration field, are observed in all cases, though unrelated particle motions are responsible for significant loss of the spatio-temporal coherence of the waves. The wave speed was determined from repeated space–time autocorrelations of the local concentration field and appears in reasonable agreement with Kynch sedimentation theory using the Richardson–Zaki relation. The passage of kinematic waves causes perturbations in the particle velocity at a frequency that matches well with peak frequencies in the particle velocity spectra for concentrations up to ϕ≈10%. The time-lagged cross-correlation of the vertical and horizontal particle velocity suggests that kinematic waves may trigger DKT instabilities, while conversely DKT instabilities may be responsible for the onset of kinematic waves. Finally, we suggest that obstruction and perturbation of the particle wake by neighboring particles could offer an explanation for the small influence of the Galileo number on the suspension behavior for ϕ=2−30%.","Drafting–kissing–tumbling; Kinematic waves; Particle interactions; Sedimentation; Wake trapping","en","journal article","","","","","","","","","","","Multi Phase Systems","","",""
"uuid:56f36880-d8f0-442f-8403-f77b58eda04f","http://resolver.tudelft.nl/uuid:56f36880-d8f0-442f-8403-f77b58eda04f","Numerical study of a pair of spheres in an oscillating box filled with viscous fluid","Van Overveld, T. J.J.M. (Eindhoven University of Technology); Shajahan, M.T. (TU Delft Multi Phase Systems); Breugem, W.P. (TU Delft Multi Phase Systems); Clercx, H. J.H. (Eindhoven University of Technology); Duran-Matute, M. (Eindhoven University of Technology)","","2022","When two spherical particles submerged in a viscous fluid are subjected to an oscillatory flow, they align themselves perpendicular to the direction of the flow leaving a small gap between them. The formation of this compact structure is attributed to a nonzero residual flow known as steady streaming. We have performed direct numerical simulations of a fully resolved, oscillating flow in which the pair of particles is modeled using an immersed boundary method. Our simulations show that the particles oscillate both parallel and perpendicular to the oscillating flow in elongated figure-8 trajectories. In absence of bottom friction, the mean gap between the particles depends only on the normalized Stokes boundary layer thickness δ∗, and on the normalized, streamwise excursion length of the particles relative to the fluid Ar∗ (equivalent to the Keulegan-Carpenter number). For Ar∗≲1, viscous effects dominate and the mean particle separation only depends on δ∗. For larger Ar∗ values, advection becomes important and the gap widens. Overall, the normalized mean gap between the particles scales as L∗≈3.0δ∗1.5+0.03Ar∗3, which also agrees well with previous experimental results. The two regimes are also observed in the magnitude of the oscillations of the gap perpendicular to the flow, which increases in the viscous regime and decreases in the advective regime. When bottom friction is considered, particle rotation increases and the gap widens. Our results stress the importance of simulating the particle motion with all its degrees of freedom to accurately model the system and reproduce experimental results. The insights of the particle pairs provide an important step towards understanding denser and more complex systems.","","en","journal article","","","","","","","","","","","Multi Phase Systems","","",""
"uuid:4d4aa9eb-708c-4706-8669-37c10e90ea27","http://resolver.tudelft.nl/uuid:4d4aa9eb-708c-4706-8669-37c10e90ea27","Effect of the Stokes boundary layer on the dynamics of particle pairs in an oscillatory flow","Van Overveld, T. J.J.M. (Eindhoven University of Technology); Breugem, W.P. (TU Delft Multi Phase Systems); Clercx, Herman J.H. (Eindhoven University of Technology); Duran-Matute, M. (Eindhoven University of Technology)","","2022","The alignment of a pair of spherical particles perpendicular to a horizontally oscillating flow is attributed to a non-zero residual flow, known as steady streaming. This phenomenon is the basis of complex patterns in denser systems, such as particle chains and the initial stages of rolling-grain ripples. Previous studies on such self-organization processes used two distinct systems: an oscillating box filled with viscous fluid and an oscillating channel flow, where the fluid oscillates relative to the bottom boundary. In this paper, we show that particle pair dynamics in these two systems are fundamentally different, due to the presence of a Stokes boundary layer above the bottom in the oscillating channel flow. The results are obtained from direct numerical simulations in which the dynamics of a pair of particles are simulated using an immersed boundary method. The oscillating box and the oscillating channel flow are only equivalent in a limited region of the parameter space, where both the normalized Stokes boundary layer thickness and the normalized relative particle excursion length are small. Overall, the particle dynamics in the oscillating channel flow, compared to the oscillating box, are governed by an additional dimensionless parameter, that is, the particle–fluid density ratio.","","en","journal article","","","","","","Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.","","2023-07-01","","","Multi Phase Systems","","",""
"uuid:74cec1a7-c6e0-4ab1-b4eb-972e6437e42c","http://resolver.tudelft.nl/uuid:74cec1a7-c6e0-4ab1-b4eb-972e6437e42c","Path instabilities of a freely rising or falling sphere","Kaveripuram Ramasamy, S.R. (TU Delft Wind Energy); Poelma, C. (TU Delft Process and Energy); Breugem, W.P. (TU Delft Multi Phase Systems)","","2022","Path instabilities of a sphere rising or falling in a quiescent Newtonian fluid have been studied experimentally. The rich palette of possible instabilities is dependent upon two dimensionless quantities, namely the Galileo number (Ga) and the particle/fluid mass density ratio (ρ¯). In recent literature, several (Ga,ρ¯) regime maps have been proposed to characterize path instabilities, based on both numerical and experimental studies, with substantial disagreements among them. The present study attempts to shed light on path instabilities for which previous studies disagree. A detailed experimental investigation has been conducted for 219 different combinations of Ga and ρ¯, grouped around four values of ρ¯ (∼ 0.87, 1.12, 3.19 and 3.9) and Ga in the range of ∼ 100 to 700. Our results agree well with literature for the low Ga range in which a particle takes a steady vertical or steady oblique path and for which all previous studies agree with each other. For the higher and more controversial Ga range, we discuss consensus and disagreements with previous studies. Some regimes, which were only recently observed in numerical simulations, have been observed experimentally for the first time. Also, intriguing bi-stable regimes (i.e., coexistence of two stable asymptotic states) have been observed. For all four investigated density ratios, an update of the regime map is proposed. Finally, for both the rising and falling spheres, the drag coefficient as function of terminal settling Reynolds number has been determined, which for the investigated density ratios does not differ significantly from that of flow past a fixed sphere.","Freely rising/falling sphere; Particle tracking velocimetry; Path instability; Regime map; Wake instability","en","journal article","","","","","","","","","","Process and Energy","Wind Energy","","",""
"uuid:0ff591bf-b113-4f46-9fd0-2cddb9b4cacc","http://resolver.tudelft.nl/uuid:0ff591bf-b113-4f46-9fd0-2cddb9b4cacc","A novel sensor measuring local voidage profile inside a fluidised bed reactor","Kramer, O.J.I. (TU Delft Complex Fluid Processing; Waternet; Hogeschool Utrecht; Queen Mary University of London); van Schaik, C. (Waternet; Hogeschool Utrecht); Hangelbroek, J.J. (Waternet); de Moel, P.J. (TU Delft Sanitary Engineering; Waternet; Omnisys); Colin, M.G. (Waternet); Amsing, M. (Bienfait); Boek, E.S. (Queen Mary University of London); Breugem, W.P. (TU Delft Multi Phase Systems); Padding, J.T. (TU Delft Complex Fluid Processing); van der Hoek, J.P. (TU Delft Sanitary Engineering; Waternet)","","2021","Liquid-solid fluidisation is frequently encountered in drinking water treatment processes, often to obtain a large liquid-solid interfacial surface area. A large surface area is crucial for optimal seeded crystallisation in full-scale softening reactors. Due to crystallisation, particles grow and migrate to a lower zone in the reactor which leads to a stratified bed. Larger particles adversely affect the surface area. To maintain optimal process conditions in the fluidised beds, information is needed about the distribution of particle size, local voidage and available surface area, over the reactor height.
In this work, a sensor is developed to obtain the hydraulic state gradient, based on Archimedes’ principle. A cylindrical heavy object is submerged in the fluidised bed and lowered gradually while its weight is measured at various heights using a sensitive force measuring device.
Based on accurate fluidisation experiments with calcite grains, the voidage is determined and a straightforward empirical model is developed to estimate the particle size as a function of superficial fluid velocity, kinematic viscosity, suspension density, voidage and particle density. The surface area and specific space velocity can be estimated accordingly, which represent key performance indicators regarding the hydraulic state of the fluidised bed reactor. The prediction error for voidage is 5 ± 2 % and for particle size 9 ± 4 %.
The newly developed soft sensor is a more time-effective method for obtaining the hydraulic state in full-scale liquid-solid fluidised bed reactors.","Fluidization; Drinking water treatment; Pellet-softening; Hydrostatic soft sensor; Hydraulic state","en","journal article","","","","","","","","","","","Complex Fluid Processing","","",""
"uuid:32e54276-6e69-4899-b60a-ac745a0c42c0","http://resolver.tudelft.nl/uuid:32e54276-6e69-4899-b60a-ac745a0c42c0","Can terminal settling velocity and drag of natural particles in water ever be predicted accurately?","Kramer, O.J.I. (TU Delft Complex Fluid Processing; Waternet; Hogeschool Utrecht); de Moel, Peter J. (Omnisys VOF); Kaveripuram Ramasamy, S.R. (TU Delft Fluid Mechanics); Baars, Eric T. (Waternet); van Vught, Wim H. (Hogeschool Utrecht); Breugem, W.P. (TU Delft Multi Phase Systems); Padding, J.T. (TU Delft Complex Fluid Processing); van der Hoek, J.P. (TU Delft Sanitary Engineering; Waternet)","","2021","Natural particles are frequently applied in drinking water treatment processes in fixed bed reactors, fluidised bed reactors, and sedimentation processes to clarify water and to concentrate solids. When particles settle, it has been found that, in terms of hydraulics, natural particles behave differently when compared to perfectly round spheres. To estimate the terminal settling velocity of single solid particles in a liquid system, a comprehensive collection of equations is available. For perfectly round spheres, the settling velocity can be calculated quite accurately. However, for naturally polydisperse non-spherical particles, experimentally measured settling velocities of individual particles show considerable spread from the calculated average values.
This work aims to analyse and explain the different causes of this spread. To this end, terminal settling experiments were conducted in a quiescent fluid with particles varying in density, size, and shape. For the settling experiments, opaque and transparent spherical polydisperse and monodisperse glass beads were selected. In this study, we also examined drinking-water-related particles, like calcite pellets and crushed calcite seeding material grains, which are both applied in drinking water softening. Polydisperse calcite pellets were sieved and separated to acquire more uniformly dispersed samples. In addition, a wide variety of grains with different densities, sizes, and shapes were investigated for their terminal settling velocity and behaviour. The derived drag coefficient was compared with well-known models such as the one of Brown and Lawler (2003).
A sensitivity analysis showed that the spread is caused, to a lesser extent, by variations in fluid properties, measurement errors, and wall effects. Natural variations in specific particle density, path trajectory instabilities, and distinctive multi-particle settling behaviour caused a slightly larger degree of the spread. In contrast, a greater spread is caused by variations in particle size, shape, and orientation.
In terms of robust process designs and adequate process optimisation for fluidisation and sedimentation of natural granules, it is therefore crucial to take into consideration the influence of the natural variations in the settling velocity when using predictive models of round spheres.","","en","journal article","","","","","","","","","","","Complex Fluid Processing","","",""
"uuid:4f943a90-4782-49be-8402-98d4a68bb58d","http://resolver.tudelft.nl/uuid:4f943a90-4782-49be-8402-98d4a68bb58d","Active control of jet breakup and droplet formation using temperature modulation","Kamis, Y.E. (TU Delft Multi Phase Systems); Eral, H.B. (TU Delft Complex Fluid Processing); Breugem, W.P. (TU Delft Multi Phase Systems)","","2021","Using a slender-jet approach, we numerically investigate the control of jet breakup using temperature modulation at the nozzle with a specified frequency and amplitude. Our results show that temperature modulation does lead to instability through capillary and Marangoni stresses, providing control of the droplet formation in terms of intact length and resultant drop size distribution, which is otherwise irregular due to inevitable presence of background noise. For understanding the mechanisms underpinning the breakup of a thermally modulated jet in the presence of noise, it is useful to decompose the surface tension forces into a contribution from curvature-gradient forces and a contribution from surface tension-gradient forces, associated with axial variations in the jet curvature and the temperature-dependent surface tension coefficient, respectively. We show that in the limit of slow axial heat diffusion and slow cooling to the ambient, as considered here, the breakup of a thermally modulated jet is governed by the ratio of the surface tension-gradient force to the imposed random perturbation force at nozzle exit. This so-called “thermal modulation strength number” depends on the amplitude and frequency of the thermal modulation, the sensitivity of the surface tension coefficient to variations in temperature, the Weber number, and the strength of the Gaussian white noise added to the nozzle exit velocity. We show that the thermal modulation strength number governs the shift in breakup characteristics from forward to rear pinchoff for increasing modulation strength as well as the nature of the instability. When thermal modulation is weak, the surface tension-gradient forces act only as a trigger, and curvature-gradient forces soon take over and grow exponentially downstream from the jet due to inertio-capillary growth. When thermal modulation is strong, the surface tension-gradient forces not only act as a trigger, but remain significant until breakup. The thermal modulation strength number is thus useful to the design of thermal modulation in practical applications as a possible alternative to often-used mechanical excitation mechanisms to control jet breakup.","","en","journal article","","","","","","","","","","","Multi Phase Systems","","",""
"uuid:c3a34572-0191-4638-90e3-7a50877be146","http://resolver.tudelft.nl/uuid:c3a34572-0191-4638-90e3-7a50877be146","The influence of a porous, compliant layer with overlying discrete roughness elements as exhaust pipe wall on friction and heat transfer","Reurings, C. (TU Delft Structural Integrity & Composites); Koussios, S. (TU Delft Aerospace Manufacturing Technologies); Bergsma, O.K. (TU Delft Structural Integrity & Composites); Breugem, W.P. (TU Delft Multi Phase Systems); Vergote, K. (BOSAL ECS n.v.); Paeshuyse, L. (BOSAL ECS n.v.); Benedictus, R. (TU Delft Structural Integrity & Composites)","","2020","The purpose of this work is to experimentally establish the combined influence on the flow and thermal resistance of an exhaust pipe wall formed by a porous, compliant layer with overlying discrete roughness elements exposed to the pulsating exhaust gas flow of a combustion engine. Through measuring the streamwise pressure drop over and radial temperature differences in different pipe samples for a range of flow states with different Reynolds numbers and non-dimensional pulsation frequencies, the effects were discerned. The configurations of the sample walls covered a range of mesh pitches, compliant-layer densities, and compliant-layer compression ratios. The (non-sinusoidally) pulsating exhaust gas flow spanned the following range: Reb (= ubD/νb) = 1⋅ 104 - 3⋅ 104, Tb = 500 - 800 ∘C, ω+(= ωνb/uτ2) = 0.003 - 0.040. The friction factors were found to be effectively constant with Reynolds number and non-dimensional pulsation frequency while the variation with insulation density/compression was not significant. Additionally, for both mesh pitches, the measured friction factors were in line with those reported in literature for similar geometries with steady flow and solid walls. Together this indicates that neither compliance nor the pulsations in the exhaust gas flow significantly affect the friction for this configuration. Comparison of the samples based on the derived thermal resistance showed a similar influence of the fluid-wall interface as for the friction. Additionally a distinct influence of compression, independent of the insulation density, was observed that increases with increasing temperature. It was concluded that the increased resistance was due to additional radiation resistance because of fibre reorientation due to compression.","","en","journal article","","","","","","","","","","","Structural Integrity & Composites","","",""
"uuid:92ca6822-ebb0-40d6-becc-5d81008f05e5","http://resolver.tudelft.nl/uuid:92ca6822-ebb0-40d6-becc-5d81008f05e5","Influence of Concentration on Sedimentation of a Dense Suspension in a Viscous Fluid","Shajahan, M.T. (TU Delft Multi Phase Systems); Breugem, W.P. (TU Delft Multi Phase Systems)","","2020","Macroscopic properties of sedimenting suspensions have been studied extensively and can be characterized using the Galileo number (Ga), solid-to-fluid density ratio (πp) and mean solid volume concentration (ϕ¯). However, the particle–particle and particle–fluid interactions that dictate these macroscopic trends have been challenging to study. We examine the effect of concentration on the structure and dynamics of sedimenting suspensions by performing direct numerical simulation based on an Immersed Boundary Method of monodisperse sedimenting suspensions of spherical particles at fixed Ga= 144 , πp= 1.5 , and concentrations ranging from ϕ¯ = 0.5 to ϕ¯ = 30 %. The corresponding particle terminal Reynolds number for a single settling particle is ReT= 186. Our simulations reproduce the macroscopic trends observed in experiments and are in good agreement with semi-empirical correlations in literature. From our studies, we observe, first, a change in trend in the mean settling velocities, the dispersive time scales and the structural arrangement of particles in the sedimenting suspension at different concentrations, indicating a gradual transition from a dilute regime (ϕ¯ ≲ 2 %) to a dense regime (ϕ¯ ≳ 10 %). Second, we observe the vertical propagation of kinematic waves as fluctuations in the local horizontally-averaged concentration of the sedimenting suspension in the dense regime.","Dense suspension; Immersed boundary method; Kinematic waves; Sedimentation","en","journal article","","","","","","","","","","","Multi Phase Systems","","",""
"uuid:e65a2050-7424-4804-b772-c88b3e767257","http://resolver.tudelft.nl/uuid:e65a2050-7424-4804-b772-c88b3e767257","Deformation of a linear viscoelastic compliant coating in a turbulent flow","Benschop, H.O.G. (TU Delft Fluid Mechanics); Greidanus, A.J. (TU Delft Fluid Mechanics); Delfos, R. (TU Delft Support Process and Energy); Westerweel, J. (TU Delft Fluid Mechanics); Breugem, W.P. (TU Delft Multi Phase Systems)","","2019","We investigate the deformation of a linear viscoelastic compliant coating in a turbulent flow for a wide range of coating parameters. A one-way coupling model is proposed in which the turbulent surface stresses are expressed as a sum of streamwise-travelling waves with amplitudes determined from the stress spectra of the corresponding flow over a rigid wall. The analytically calculated coating deformation is analysed in terms of the root-mean-square (r.m.s.) surface displacement and the corresponding point frequency spectra. The present study systematically investigates the influence of five coating properties namely density, stiffness, thickness, viscoelasticity and compressibility. The surface displacements increase linearly with the fluid/solid density ratio. They are linearly proportional to the coating thickness for thin coatings, while they become independent of the thickness for thick coatings. Very soft coatings show resonant behaviour, but the displacement for stiffer coatings is proportional to the inverse of the shear modulus. The viscoelastic loss angle has only a significant influence when resonances occur in the coating response, while Poisson's ratio has a minor effect for most cases. The modelled surface displacement is qualitatively compared with recent measurements on the deformation of three different coatings in a turbulent boundary-layer flow. The model predicts the order of magnitude of the surface displacement, and it captures the increase of the coating displacement with the Reynolds number and the coating softness. Finally, we propose a scaling that collapses all the experimental data for the r.m.s. of the vertical surface displacement onto a single curve.","elastic waves; flow-structure interactions; turbulent flows","en","journal article","","","","","","","","","","","Fluid Mechanics","","",""
"uuid:58b45c36-1aaa-4d36-9cbf-7f705734621f","http://resolver.tudelft.nl/uuid:58b45c36-1aaa-4d36-9cbf-7f705734621f","Assessment of numerical methods for fully resolved simulations of particle-laden turbulent flows","Brändle de Motta, J. C. (Université de Rouen; Université de Toulouse); Simões Costa, P. (TU Delft Fluid Mechanics; KTH Royal Institute of Technology); Derksen, J. J. (University of Aberdeen); Peng, C. (University of Delaware); Wang, L. P. (University of Delaware; Southern University of Science and Technology); Breugem, W.P. (TU Delft Multi Phase Systems); Estivalezes, J. L. (ONERA Centre de Toulouse; Université de Toulouse); Vincent, S. (Université Paris-Est); Climent, E. (Université de Toulouse); Fede, P. (Université de Toulouse); Barbaresco, P. (Université de Toulouse); Renon, N. (Université de Toulouse)","","2019","During the last decade, many approaches for resolved-particle simulation (RPS) have been developed for numerical studies of finite-size particle-laden turbulent flows. In this paper, three RPS approaches are compared for a particle-laden decaying turbulence case. These methods are, the Volume-of-Fluid Lagrangian method, based on the viscosity penalty method (VoF-Lag); a direct forcing Immersed Boundary Method, based on a regularized delta function approach for the fluid/solid coupling (IBM); and the Bounce Back scheme developed for Lattice Boltzmann method (LBM-BB). The physics and the numerical performances of the methods are analyzed. Modulation of turbulence is observed for all the methods, with a faster decay of turbulent kinetic energy compared to the single-phase case. Lagrangian particle statistics, such as the velocity probability density function and the velocity autocorrelation function, show minor differences among the three methods. However, major differences between the codes are observed in the evolution of the particle kinetic energy. These differences are related to the treatment of the initial condition when the particles are inserted in an initially single-phase turbulence. The averaged particle/fluid slip velocity is also analyzed, showing similar behavior as compared to the results referred in the literature. The computational performances of the different methods differ significantly. The VoF-Lag method appears to be computationally most expensive. Indeed, this method is not adapted to turbulent cases. The IBM and LBM-BB implementations show very good scaling.","Direct numerical simulations; Finite-size particles; Particle-laden flows; Turbulence","en","journal article","","","","","","Accepted Author Manuscript","","2019-10-30","","","Fluid Mechanics","","",""
"uuid:fd79dc7b-92f3-4b2f-a5bd-e72db99e6037","http://resolver.tudelft.nl/uuid:fd79dc7b-92f3-4b2f-a5bd-e72db99e6037","A dot tracking algorithm to measure free surface deformations","Charruault, F.T. (TU Delft Fluid Mechanics); Greidanus, A.J. (TU Delft Fluid Mechanics); Breugem, W.P. (TU Delft Multi Phase Systems); Westerweel, J. (TU Delft Fluid Mechanics)","Rösgen, Thomas (editor)","2018","The present study introduces an experimental technique based on a Free Surface-Synthetic Schlieren (FS-SS) method in order to characterize free surfaces subjected to strong deformations. Current synthetic Schlieren methods are based on local image correlation and thus limited to rather weak image deformations, implying that they can only resolve rather large surface wavelengths and limited wave amplitude. The present method is a substantial improvement that allows to measure much stronger image deformations, providing access to shorter surface wavelengths and larger amplitudes (i.e. larger surface curvatures).","Turbulent flow; Air-water interface; Background oriented schlieren; Free surface synthetic schlieren; DIC; PTV; DTA; Air cavity; Coating","en","conference paper","ETH Zürich","","","","","","","","","","Fluid Mechanics","","",""
"uuid:6f34f14e-cd27-44de-91a6-f9d66893c4f8","http://resolver.tudelft.nl/uuid:6f34f14e-cd27-44de-91a6-f9d66893c4f8","Drag-reducing riblets with fouling-release properties: development and testing","Benschop, H.O.G. (TU Delft Fluid Mechanics); Guerin, A. J. (Newcastle University); Brinkmann, A. (Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM); Dale, M. L. (AkzoNobel/International Paint Ltd); Finnie, A. A. (AkzoNobel/International Paint Ltd); Breugem, W.P. (TU Delft Multi Phase Systems); Clare, A. S. (Newcastle University); Stübing, D. (Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM); Price, C. (AkzoNobel/International Paint Ltd); Reynolds, K. J. (AkzoNobel/International Paint Ltd)","","2018","The manufacture and preliminary testing of a drag-reducing riblet texture with fouling-control properties is presented. The commercial fouling-release product Intersleek® 1100SR was modified to manufacture riblet-textured coatings with an embossing technology. Hydrodynamic drag measurements in a Taylor–Couette set-up showed that the modified Intersleek® riblets reduced drag by up to 6% compared to a smooth surface. Barnacle settlement assays demonstrated that the riblets did not substantially reduce the ability of Intersleek® 1100SR to prevent fouling by cyprids of Balanus amphitrite. Diatom adhesion tests revealed significantly higher diatom attachment on the riblet surface compared to smooth Intersleek® 1100SR. However, after exposure to flow, the final cell density was similar to the smooth surface. Statically immersed panels in natural seawater showed an increase of biofilm cover due to the riblets. However, the release of semi-natural biofilms grown in a multi-species biofilm culturing reactor was largely unaffected by the presence of a riblet texture.","antifouling; biofilm release; drag reduction; Intersleek®; marine coatings; Riblet texture","en","journal article","","","","","","","","","","","Fluid Mechanics","","",""
"uuid:e8b67970-9238-43f9-b105-fa2a34161a1b","http://resolver.tudelft.nl/uuid:e8b67970-9238-43f9-b105-fa2a34161a1b","Drag reduction by herringbone riblet texture in direct numerical simulations of turbulent channel flow","Benschop, H.O.G. (TU Delft Fluid Mechanics); Breugem, W.P. (TU Delft Multi Phase Systems)","","2017","A bird-feather-inspired herringbone riblet texture was investigated for turbulent drag reduction. The texture consists of blade riblets in a converging/diverging or herringbone pattern with spanwise wavelength Λf. The aim is to quantify the drag change for this texture as compared to a smooth wall and to study the underlying mechanisms. To that purpose, direct numerical simulations of turbulent flow in a channel with height Lz were performed. The Fukagata-Iwamoto-Kasagi identity for drag decomposition was extended to textured walls and was used to study the drag change mechanisms. For Λf/Lz ≳ O(10), the herringbone texture behaves similarly to a conventional parallel-riblet texture in yaw: the suppression of turbulent advective transport results in a slight drag reduction of 2%. For Λf/Lz ≲ O(1), the drag increases strongly with a maximum of 73%. This is attributed to enhanced mean and turbulent advection, which results from the strong secondary flow that forms over regions of riblet convergence/divergence. Hence, the employment of convergent/divergent riblets in the texture seems to be detrimental to turbulent drag reduction.","Drag reduction; riblets; direct numerical simulations","en","journal article","","","","","","","","","","","Fluid Mechanics","","",""
"uuid:3fbb3bec-2cd5-443b-a47f-093c53cb0466","http://resolver.tudelft.nl/uuid:3fbb3bec-2cd5-443b-a47f-093c53cb0466","Turbulence modulation by dense suspensions in channel flows","Picano, Francesco (Università degli Studi di Padova); Simões Costa, P. (TU Delft Fluid Mechanics); Breugem, W.P. (TU Delft Multi Phase Systems); Brandt, Luca (KTH Royal Institute of Technology)","","2017","Dense suspensions are usually investigated in the laminar limit where inertial effects are insignificant. In this regime, the main effect of the suspended phase is to alter the rheological behavior of the flow which always displays higher effective viscosity with respect to the carrier fluid. When the flow rate is high enough, i.e. at high Reynolds number, the flow may become turbulent and the interaction between solid and liquid phase modifies the turbulent dynamics that we know in single-phase fluids. In the present work, we study turbulent channel flows laden with finite-size particles at high volume fraction (F = 0:2) by means of Direct Numerical Simulations. A direct-forcing Immersed Boundary Method has been adopted to couple liquid and solid phases. The two-phase simulations have been performed fixing the bulk Reynolds number at Reb = Ub 2h=n = 12000 (Ub bulk velocity, h channel half-width and n the fluid kinematic viscosity). The particle size is relatively large with respect to the viscous length, i.e. 10 and 20 times, but smaller than large scales. We will present a detailed comparison of the statistical behavior of the particle-laden flow and the corresponding single-phase flow. The presence of the solid phase strongly alters the wall turbulence dynamics and its effect cannot be accounted only considering the higher rheological effective viscosity.","","en","conference paper","TSFP","","","","","","","","","","Fluid Mechanics","","",""
"uuid:d959bb0b-344d-4e68-8371-6cfa3e2f6fad","http://resolver.tudelft.nl/uuid:d959bb0b-344d-4e68-8371-6cfa3e2f6fad","Auto-generation in wall turbulence by the interaction of weak eddies","Goudar Vishwanathappa, M. (TU Delft Fluid Mechanics); Breugem, W.P. (TU Delft Multi Phase Systems); Elsinga, G.E. (TU Delft Fluid Mechanics)","","2016","For channel flow, we explore how commonly found weak eddies can still auto-generate and produce new eddies. Before, only strong eddies (above a threshold strength) were considered to auto-generate. Such strong eddies are rarely observed in actual turbulent flows however. Here, the evolution of two weak conditional eddies with different initial strengths, initial sizes, and initial stream-wise spacing between them is studied. The numerical procedure followed is similar to Zhou et al. [“Mechanisms for generating coherent packets of hairpin vortices in channel flow,” J. Fluid Mech. 387, 353 (1999)]. The two eddies are found to merge into a single stronger eddy when the initial upstream eddy is taller than the downstream eddy, which further auto-generates when the initial stream-wise separation is small (<120 wall units). However, it is observed that non-merging cases with small initial stream-wise separation also auto-generated. In the initial condition, the two conditional eddies are placed near to each other so their velocity fields (low-speed streaks and ejection events) get superimposed and amplified as a function of stream-wise spacing. To examine this effect, a divergence free low-speed streak is superimposed on an eddy. It is found that these low-speed streak simulations do not auto-generate. On the other hand, a rapid lift-up of an eddy by ejection events plays a role in the onset of auto-generation, which also leads to a modified interpretation of auto-generation mechanism. It differed from the existing auto-generation mechanism at the later stages of auto-generation where blockage of mean flow and shear layer deformation is considered instead of vortex dynamics.","Eddies; Rotating flows; Vortex interactions; Turbulent channel flow; Channel flows","en","journal article","","","","","","","","2017-03-21","","","Fluid Mechanics","","",""
"uuid:f9f54382-0bda-4a60-8535-0d09a6fd4348","http://resolver.tudelft.nl/uuid:f9f54382-0bda-4a60-8535-0d09a6fd4348","Auto-generation by interaction of weak eddies","Goudar Vishwanathappa, M. (TU Delft Fluid Mechanics); Breugem, W.P. (TU Delft Multi Phase Systems); Jodai, Y. (National College of Technology); Elsinga, G.E. (TU Delft Fluid Mechanics)","Floryan, J.M. (editor); Tvergaard, V. (editor); van Campen, D. (editor)","2016","For channel flow, we explore how the interaction of weak eddies produces additional eddies by means of auto-generation. This is done by DNS of two eddies with different initial strengths, initial sizes and initial stream-wise spacing between them. The numerical procedure followed is similar to Zhou et al[1]. The two eddies merge into a single stronger eddy when a larger upstream and a smaller downstream eddy are placed within a certain initial stream-wise separation distance. Subsequently, the resulting stronger eddy is observed to auto-generate new eddies. The non-merging cases with small initial stream wise separation also auto-generate. The auto-generation is characterized by a rapid lift-up of an initial eddy, which blocks the incoming flow and leads to shear- layer roll-up and formation of a new eddy. The same sequence of events is observed in a fully developed turbulent boundary layer[2].","auto-generation; boundary layers","en","conference paper","","","","","","","","","","","Fluid Mechanics","","",""
"uuid:c8e54a34-8471-4adc-b6f6-4caece7c28e3","http://resolver.tudelft.nl/uuid:c8e54a34-8471-4adc-b6f6-4caece7c28e3","Accurate measurements of the skin surface area of the healthy auricle and skin deficiency in microtia patients","Otto, I.A. (University Medical Center Utrecht); van Doremalen, R.F.M. (University Medical Center Utrecht); Melchels, F.P.W. (University Medical Center Utrecht); Kolodzynski, M.N. (University Medical Center Utrecht); Pouran, B. (TU Delft Biomaterials & Tissue Biomechanics; University Medical Center Utrecht); Malda, Jos (Universiteit Utrecht; University Medical Center Utrecht); Kon, M. (University Medical Center Utrecht); Breugem, C.A. (University Medical Center Utrecht; Meander Medical Center)","","2016","","","en","journal article","","","","","","","","","","","Biomaterials & Tissue Biomechanics","","",""
"uuid:fd89156a-6522-449b-aab6-d96093b5041c","http://resolver.tudelft.nl/uuid:fd89156a-6522-449b-aab6-d96093b5041c","Universal scaling laws for dense particle suspensions in turbulent wall-bounded flows","Simões Costa, P. (TU Delft Fluid Mechanics); Picano, Francesco (Università degli Studi di Padova); Brandt, Luca (KTH Royal Institute of Technology); Breugem, W.P. (TU Delft Multi Phase Systems; TU Delft Fluid Mechanics)","","2016","The macroscopic behavior of dense suspensions of neutrally buoyant spheres in turbulent plane channel flow is examined. We show that particles larger than the smallest turbulence scales cause the suspension to deviate from the continuum limit in which its dynamics is well described by an effective suspension viscosity. This deviation is caused by the formation of a particle layer close to the wall with significant slip velocity. By assuming two distinct transport mechanisms in the near-wall layer and the turbulence in the bulk, we define an effective wall location such that the flow in the bulk can still be accurately described by an effective suspension viscosity. We thus propose scaling laws for the mean velocity profile of the suspension flow, together with a master equation able to predict the increase in drag as a function of the particle size and volume fraction.","","en","journal article","","","","","","","","","","","Fluid Mechanics","","",""
"uuid:66d319a3-fa31-4cee-b397-649ce28f5b82","http://resolver.tudelft.nl/uuid:66d319a3-fa31-4cee-b397-649ce28f5b82","Collision model for fully resolved simulations of flows laden with finite-size particles","Costa, P.; Boersma, B.J.; Westerweel, J.; Breugem, W.P.","","2015","We present a collision model for particle-particle and particle-wall interactions in interface-resolved simulations of particle-laden flows. Three types of interparticle interactions are taken into account: (1) long- and (2) short-range hydrodynamic interactions, and (3) solid-solid contact. Long-range interactions are incorporated through an efficient and second-order-accurate immersed boundary method (IBM). Short-range interactions are also partly reproduced by the IBM. However, since the IBM uses a fixed grid, a lubrication model is needed for an interparticle gap width smaller than the grid spacing. The lubrication model is based on asymptotic expansions of analytical solutions for canonical lubrication interactions between spheres in the Stokes regime. Roughness effects are incorporated by making the lubrication correction independent of the gap width for gap widths smaller than ?1% of the particle radius. This correction is applied until the particles reach solid-solid contact. To model solid-solid contact we use a variant of a linear soft-sphere collision model capable of stretching the collision time. This choice is computationally attractive because it allows us to reduce the number of time steps required for integrating the collision force accurately and is physically realistic, provided that the prescribed collision time is much smaller than the characteristic time scale of particle motion. We verified the numerical implementation of our collision model and validated it against several benchmark cases for immersed head-on particle-wall and particle-particle collisions, and oblique particle-wall collisions. The results show good agreement with experimental data.","","en","journal article","American Physical Society","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:f51259c7-cce5-435a-99d1-1863b2b4e632","http://resolver.tudelft.nl/uuid:f51259c7-cce5-435a-99d1-1863b2b4e632","Mechanics of dense suspensions in turbulent channel flows","Picano, F.; Costa, P.; Breugem, W.P.; Brandt, L.","","2015","Dense suspensions are usually investigated in the laminar limit where inertial effects are insignificant. When the flow rate is high enough, i.e. at high Reynolds number, the flow may become turbulent and the interaction between solid and liquid phases modifies the turbulence we know in single-phase fluids. In the present work, we study turbulent channel flows laden with finite-size particles at high volume fraction by means of Direct Numerical Simulations. A direct-forcing Immersed Boundary Method has been adopted to couple liquid and solid phases. We will show that the turbulence is attenuated in dense cases, even though the overall drag is increased because of the particle contribution to the total stress.","","en","conference paper","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:b5d41ec2-420d-4ade-afd5-67a1966a28aa","http://resolver.tudelft.nl/uuid:b5d41ec2-420d-4ade-afd5-67a1966a28aa","Mechanics of dense suspensions in turbulent channel flows","Picano, F.; Costa, P.; Breugem, W.P.; Brandt, L.","Picano, F. (author); Costa, P. (author); Breugem, W.P. (author); Brandt, L. (author)","2015","Dense suspensions are usually investigated in the laminar limit where inertial effects are insignificant. When the flow rate is high enough, i.e. at high Reynolds number, the flow may become turbulent and the interaction between solid and liquid phases modifies the turbulence we know in single-phase fluids. In the present work, we study turbulent channel flows laden with finite-size particles at high volume fraction by means of Direct Numerical Simulations. A direct-forcing Immersed Boundary Method has been adopted to couple liquid and solid phases. We will show that the turbulence is attenuated in dense cases, even though the overall drag is increased because of the particle contribution to the total stress.","","en","conference paper","","","","","","","","","","","","","",""
"uuid:73746d45-6c4a-45aa-bbb9-f3d5293788a5","http://resolver.tudelft.nl/uuid:73746d45-6c4a-45aa-bbb9-f3d5293788a5","Structure and dynamics of turbulent flows over highly permeable walls","Breugem, W.P.; Ardekani, M.N.; Elsinga, G.E.","Breugem, W.P. (author); Ardekani, M.N. (author); Elsinga, G.E. (author)","2015","Highly porous materials are found in various industrial applications and environmental flows. In previous studies it was found that a turbulent flow along a highly porous wall experiences a higher skin friction as compared to a solid wall with similar surface roughness when the so-called permeability Reynolds number (Re_K) is larger than O(1). The main objective of the present study was to gain understanding of the characteristic structures and auto-generation mechanisms of turbulence for Re_K >> 1. To this purpose the Volume-Averaged Navier-Stokes (VANS) equations were solved in a Direct Numerical Simulation (DNS) of a turbulent flow through a plane channel with an upper solid wall and a lower porous wall at Re_K = 5.91. The DNS results are in good agreement with available Particle Image Velocimetry (PIV) data for the same flow geometry. A linear stochastic estimation technique was used to capture the structure associated with the characteristic ejection event that contributes most to the Reynolds shear stress near the porous wall. This structure is similar to a horseshoe vortex. Contrary to the conventional hairpin vortex found near solid walls, this horseshoe vortex has a significantly higher inclination angle with the wall and its legs are much shorter. The latter is consistent with the observed absence of low and high-speed streaks near highly permeable walls. Next, the auto-generation mechanisms of the horseshoe vortex were studied in another DNS in which the horseshoe vortex was released in the Reynolds-averaged flow field obtained from the former DNS. Two distinct auto-generation mechanisms were observed: (1) the generation of new structures at the upstream end of the horseshoe vortex, which evolve rapidly into a turbulent spot with an arrowhead shape, and (2) the interaction of the horseshoe vortex with spanwise oriented Kelvin-Helmholtz vortex rollers originating from the inflexion point in the mean velocity profile near the porous wall.","","en","conference paper","","","","","","","","","","","","","",""
"uuid:793f82e1-35d8-4b15-92f7-5020bfa970b2","http://resolver.tudelft.nl/uuid:793f82e1-35d8-4b15-92f7-5020bfa970b2","Direct numerical simulations of drag reduction in turbulent channel flow over bio-inspired herringbone riblet-texture","Benschop, H.O.G.; Westerweel, J.; Breugem, W.P.","","2015","The use of drag reducing surface textures is a promising passive method to reduce fuel consumption. Probably most wellknown is the utilisation of shark-skin inspired ridges or riblets parallel to the mean flow. They can reduce drag up to 10%. Recently another bio-inspired texture based on bird flight feather riblets has been proposed. It differs from the standard riblets in two ways. First, the riblets are arranged in a converging/diverging or herringbone pattern. Second, the riblet height or groove depth changes gradually. Drag reductions as high as 20% have been claimed [2]. The objective of the present work is to study the drag reducing properties and mechanisms of this texture. To that purpose Direct Numerical Simulations (DNSs) of turbulent plane channel flow have been performed. Structured roughness has been applied to both walls and several geometric parameters have been varied. Marginal drag reductions on the order of 2.5% and significant drag increases well beyond 100% were found. The latter is attributed to a strong secondary flow that mixes momentum through the whole channel. In future optimization studies we might look for conditions at which secondary motions affect the near-wall cycle of turbulence only.","","en","conference paper","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:48389198-6af2-4fb1-9be4-dc39ee6fe173","http://resolver.tudelft.nl/uuid:48389198-6af2-4fb1-9be4-dc39ee6fe173","Direct numerical simulations of drag reduction in turbulent channel flow over bio-inspired herringbone riblet-texture","Benschop, H.O.G.; Westerweel, J.; Breugem, W.P.","Benschop, H.O.G. (author); Westerweel, J. (author); Breugem, W.P. (author)","2015","The use of drag reducing surface textures is a promising passive method to reduce fuel consumption. Probably most wellknown is the utilisation of shark-skin inspired ridges or riblets parallel to the mean flow. They can reduce drag up to 10%. Recently another bio-inspired texture based on bird flight feather riblets has been proposed. It differs from the standard riblets in two ways. First, the riblets are arranged in a converging/diverging or herringbone pattern. Second, the riblet height or groove depth changes gradually. Drag reductions as high as 20% have been claimed [2]. The objective of the present work is to study the drag reducing properties and mechanisms of this texture. To that purpose Direct Numerical Simulations (DNSs) of turbulent plane channel flow have been performed. Structured roughness has been applied to both walls and several geometric parameters have been varied. Marginal drag reductions on the order of 2.5% and significant drag increases well beyond 100% were found. The latter is attributed to a strong secondary flow that mixes momentum through the whole channel. In future optimization studies we might look for conditions at which secondary motions affect the near-wall cycle of turbulence only.","","en","conference paper","","","","","","","","","","","","","",""
"uuid:72c5393c-ba84-472b-97bc-73dab7445a26","http://resolver.tudelft.nl/uuid:72c5393c-ba84-472b-97bc-73dab7445a26","Flow regimes of inertial suspensions of finite size particles","Lashgari, I.; Picano, F.; Breugem, W.P.; Brandt, L.","Lashgari, I. (author); Picano, F. (author); Breugem, W.P. (author); Brandt, L. (author)","2015","Inertial regimes in a channel flow of suspension of finite-size neutrally buoyant particles are studied for a wide range of Reynolds numbers: $500 \le Re\le 5000$, and particle volume fractions: $0 \le \Phi \le 0.3$. The flow is classified in three different regimes according to the phase-averaged stress budget across the channel \cite{Lashgari2014}. The laminar viscous regime at low $Re$ and $\Phi$ where the viscous stress is the dominating term in the budget, the turbulent regime at high $Re$ and relatively low $\Phi$ where the momentum is mainly transferred by the action of the Reynolds stress and the inertial shear-thickening regime where the particle stress contributes the most to the significant enhancement of the wall shear stress. Particle distribution and dispersion properties provide additional evidence for the existence of the three different regimes.","","en","conference paper","","","","","","","","","","","","","",""
"uuid:386b529b-7cc9-4672-9600-93a6a3916980","http://resolver.tudelft.nl/uuid:386b529b-7cc9-4672-9600-93a6a3916980","Flow regimes of inertial suspensions of finite size particles","Lashgari, I.; Picano, F.; Breugem, W.P.; Brandt, L.","","2015","Inertial regimes in a channel flow of suspension of finite-size neutrally buoyant particles are studied for a wide range of Reynolds numbers: 500 Re 5000, and particle volume fractions: 0 0:3. The flow is classified in three different regimes according to the phase-averaged stress budget across the channel [2]. The laminar viscous regime at low Re and - where the viscous stress is the dominating term in the budget, the turbulent regime at high Re and relatively low where the momentum is mainly transferred by the action of the Reynolds stress and the inertial shear-thickening regime where the particle stress contributes the most to the significant enhancement of the wall shear stress. Particle distribution and dispersion properties provide additional evidence for the existence of the three different regimes.","","en","conference paper","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:5a1b2763-4b90-411b-9cd9-93a760207ed8","http://resolver.tudelft.nl/uuid:5a1b2763-4b90-411b-9cd9-93a760207ed8","Transition to Turbulence in the Presence of Finite Size Particles","Lashgari, I.; Picano, F.; Breugem, W.P.; Brandt, L.","","2015","We study the transition from laminar to turbulent flow in a channel seeded with finite-size neutrally buoyant particles. A fixed ratio of 10 between the channel height and the particle diameter is considered. The flow is examined in the range of Reynolds numbers 500 ? Re ? 5000 and the particle volume fractions 0.001 ? ? ? 0.3. We report a non-monotonic behavior of the threshold value of the Reynolds number above which the flow becomes turbulent, in agreement with previous experimental studies. The mean square velocity fluctuations and Reynolds shear stress of the fluid phase are reduced by increasing the particle volume fraction at a fixed Re=1500, while the mean square velocities of the solid phase are enhanced monotonically suggesting a transition from fluid to particle dominated dynamics at high volume fraction.","transition; finite-size particles; inertial suspensions","en","journal article","Elsevier","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:1d714332-1b46-4c7b-b3d2-b36b8f1c848e","http://resolver.tudelft.nl/uuid:1d714332-1b46-4c7b-b3d2-b36b8f1c848e","Laminar, turbulent, and inertial shear-thickening regimes in channel flow of neutrally buoyant particle suspensions","Lashgari, I.; Picano, F.; Breugem, W.P.; Brandt, L.","","2014","The aim of this Letter is to characterize the flow regimes of suspensions of finite-size rigid particles in a viscous fluid at finite inertia. We explore the system behavior as a function of the particle volume fraction and the Reynolds number (the ratio of flow and particle inertia to viscous forces). Unlike single-phase flows, where a clear distinction exists between the laminar and the turbulent states, three different regimes can be identified in the presence of a particulate phase, with smooth transitions between them. At low volume fractions, the flow becomes turbulent when increasing the Reynolds number, transitioning from the laminar regime dominated by viscous forces to the turbulent regime characterized by enhanced momentum transport by turbulent eddies. At larger volume fractions, we identify a new regime characterized by an even larger increase of the wall friction. The wall friction increases with the Reynolds number (inertial effects) while the turbulent transport is weakly affected, as in a state of intense inertial shear thickening. This state may prevent the transition to a fully turbulent regime at arbitrary high speed of the flow.","","en","journal article","American Physical Society","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:e15c9b8b-5ac0-4760-89c2-e18ca748083c","http://resolver.tudelft.nl/uuid:e15c9b8b-5ac0-4760-89c2-e18ca748083c","Active suspensions in thin films: Nutrient uptake and swimmer motion","Lambert, R.A.; Picano, F.; Breugem, W.P.; Brandt, L.","","2013","A numerical study of swimming particle motion and nutrient transport is conducted for a semidilute to dense suspension in a thin film. The steady squirmer model is used to represent the motion of living cells in suspension with the nutrient uptake by swimming particles modelled using a first-order kinetic equation representing the absorption process that occurs locally at the particle surface. An analysis of the dynamics of the neutral squirmers inside the film shows that the vertical motion is reduced significantly. The mean nutrient uptake for both isolated and populations of swimmers decreases for increasing swimming speeds when nutrient advection becomes relevant as less time is left for the nutrient to diffuse to the surface. This finding is in contrast to the case where the uptake is modelled by imposing a constant nutrient concentration at the cell surface and the mass flux results to be an increasing monotonic function of the swimming speed. In comparison to non-motile particles, the cell motion has a negligible influence on nutrient uptake at lower particle absorption rates since the process is rate limited. At higher absorption rates, the swimming motion results in a large increase in the nutrient uptake that is attributed to the movement of particles and increased mixing in the fluid. As the volume fraction of swimming particles increases, the squirmers consume slightly less nutrients and require more power for the same swimming motion. Despite this increase in energy consumption, the results clearly demonstrate that the gain in nutrient uptake make swimming a winning strategy for micro-organism survival also in relatively dense suspensions.","biological fluid dynamics; micro-organism dynamics; multiphse and particle-laden flows","en","journal article","Cambridge University Press","","","","","","","2014-09-24","Mechanical, Maritime and Materials Engineering","Process & Energy","","","",""
"uuid:bb3efe10-704f-4201-806a-63ca4c744ee3","http://resolver.tudelft.nl/uuid:bb3efe10-704f-4201-806a-63ca4c744ee3","Shear Thickening in Non-Brownian Suspensions: An Excluded Volume Effect","Picano, F.; Breugem, W.P.; Mitra, D.; Brandt, L.","","2013","Shear thickening appears as an increase of the viscosity of a dense suspension with the shear rate, sometimes sudden and violent at high volume fraction. Its origin for noncolloidal suspension with non-negligible inertial effects is still debated. Here we consider a simple shear flow and demonstrate that fluid inertia causes a strong microstructure anisotropy that results in the formation of a shadow region with no relative flux of particles. We show that shear thickening at finite inertia can be explained as an increase of the effective volume fraction when considering the dynamically excluded volume due to these shadow regions.","","en","journal article","American Physical Society","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:9009251e-4fe5-46d2-8f32-d38c9fa07945","http://resolver.tudelft.nl/uuid:9009251e-4fe5-46d2-8f32-d38c9fa07945","Numerical modelling of finite-size particle collisions in a viscous fluid","Brändle de Motta, J.C.; Breugem, W.P.; Gazanion, B.; Estivalezes, J.L.; Vincent, S.; Climent, E.","","2013","A general model is presented for short-range hydrodynamic interactions and head-on particle-particle/wall collisions. The model has been embedded in two distinct numerical methods for fully resolved simulation of finite-size particles in a viscous fluid. It accounts for the material properties of the particles and lubrication effects prior to collision that cannot be fully resolved on a fixed grid. We demonstrate that the model is able to reproduce experimental data for the coefficient of restitution of particle-wall collisions over a wide range of Stokes number based on the particle impact velocity. The set of model parameters we selected and more generally the modelling approach we propose can be efficiently used for fully resolved simulations of moderately dense solid-liquid suspensions.","flow simulation; hydrodynamics; lubrication; Navier-Stokes equations; numerical analysis; two-phase flow","en","journal article","American Institute of Physics","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:5263e887-cbb3-477e-acfd-523c1ead1cc3","http://resolver.tudelft.nl/uuid:5263e887-cbb3-477e-acfd-523c1ead1cc3","A second-order accurate Immersed Boundary Method combined with a soft-sphere collision model for fully-resolved simulations of particle-laden flows","Breugem, W.P.; Simões Costa, P.","","2013","","","en","conference paper","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:612035c1-96ce-41ad-911e-95b59fb579b3","http://resolver.tudelft.nl/uuid:612035c1-96ce-41ad-911e-95b59fb579b3","DNS of turbulent channel flows laden with finite-size particles at high volume fractions: Extended abstract","Francesco, Picano (KTH Royal Institute of Technology); Breugem, W.P. (TU Delft Multi Phase Systems); Luca, Brandt (KTH Royal Institute of Technology)","","2013","Suspensions are often found in different processes and applications, e.g. sediment transport in environments or pharmaceutical engineering. The laminar regime in the semi-dilute or dense cases, non vanishing volume fraction, is usually characterized by the sometime spectacular rheological properties induced by the suspended phase. Much less is known about dissipation and mixing in the turbulent regime. The aim of the present work is to investigate the turbulent channel flow of a fluid laden with rigid spherical particles at a fixed bulk Reynolds number Reh = U0h/ν = 2800. The particle radius is selected to be 18 times smaller than the channel half-width. Fully-resolved Direct Numerical Simulations with particle tracking and Immersed Boundary Method are presented for values of the volume fraction up to φ = 0.2. As expected for “large” particles, the overall drag increases with the volume fraction. We show that the presence of the particles deeply changes flow behavior, as already evident from the mean velocity profile with the canonical regions, buffer- or log-layer, strongly altered.","","en","conference paper","Zakon Group","","","","","","","","","","Multi Phase Systems","","",""
"uuid:3a597fae-87d4-4f84-b60c-2462fd208de5","http://resolver.tudelft.nl/uuid:3a597fae-87d4-4f84-b60c-2462fd208de5","Merging and auto-generation of vortices in wall bounded flows","Goudar Vishwanathappa, M. (TU Delft Fluid Mechanics); Breugem, W.P. (TU Delft Fluid Mechanics); Elsinga, G.E. (TU Delft Fluid Mechanics)","Johansson, AV (editor); Friedrich, R (editor); Tavoularis, S (editor)","2013","For channel flow, we explore how a hairpin eddy may reach a threshold strength required to produce additional hairpins by means of auto-generation. This is done by studying the interaction of two eddies with different initial strengths (but both below the threshold strength), initial sizes and initial streamwise spacing between them. The numerical procedure followed is similar to Zhou et al. (1999). The two eddies were found to merge into a single stronger
eddy in case of a larger upstream and a smaller downstream eddy placed within a certain initial streamwise separation distance. Subsequently, the resulting stronger eddy was observed to auto-generate new eddies. Merging of eddies thus is a viable explanation for the creation of the threshold strength eddies.","","en","conference paper","Technical University of Munich","","","","","","","","","","Fluid Mechanics","","",""
"uuid:3fa8d72d-c3aa-4786-a321-41433ad1df78","http://resolver.tudelft.nl/uuid:3fa8d72d-c3aa-4786-a321-41433ad1df78","Transport of suspended particles in turbulent open channel flows","Breugem, W.A.","Uijttewaal, W.S.J. (promotor); Stelling, G.S. (promotor)","2012","Two experiments are performed in order to investigate suspended sediment transport in a turbulent open channel flow. The first experiment used particle image velocimetry (PIV) to measure the fluid velocity with a high spatial resolution, while particle tracking velocimetry (PTV) was used to measure the velocity of individual sediment particles. The sediment particles were injected in the flume close to the free surface at different distances from the measurement section. In this way, the development of a sediment plume towards an equilibrium situation could be studied. The results were compared with direct numerical simulations, in which the particle equation of motion was used to calculate the movement of individual sediment particles. The second experiment used refractive index matching, in order to make the sediment particle invisible. In this way, a PIV experiment could be performed in order to determine changes in the flow and turbulence structure due to high sediment concentrations.","sediment transport; PIV; PTV; refractive index matching; coherent structures; turbulence; DNS; two way coupling","en","doctoral thesis","","","","","","","","","Civil Engineering and Geosciences","Hydraulic Engineering","","","",""
"uuid:a3dfebec-8e68-4255-9119-314cf992c6cd","http://resolver.tudelft.nl/uuid:a3dfebec-8e68-4255-9119-314cf992c6cd","A continuum model for flow induced by metachronal coordination between beating cilia","Hussong, J.; Breugem, W.P.; Westerweel, J.","","2011","In this numerical study we investigate the flow induced by metachronal coordination between beating cilia arranged in a densely packed layer by means of a continuum model. The continuum approach allows us to treat the problem as two-dimensional as well as stationary, in a reference frame moving with the speed of the metachronal wave. The model is used as a computationally efficient design tool to investigate cilia-induced transport of a Newtonian fluid in a plane channel. Contrary to prior continuum models, the present approach accounts for spatial variations in the porosity along the metachronal wave and thus ensures conservation of mass within the cilia layer. Using porous-media theory the governing volume-averaged Navier–Stokes (VANS) equations are derived and closure formulations are given explicitly for the model. This makes it possible to investigate cilia-induced flow with a continuum model in both the viscous regime and the inertial regime. The results show that metachronal coordination can act as a transport mechanism in both regimes. Porosity variations appear to be the key mechanism for correct prediction of the fluid transport in the viscous flow regime. The reason is that spatial variations in the porosity break the symmetry of the drag distribution along the metachronal wave. A new insight that has been gained is that the fluid transport reverses, thus switches from plectic to antiplectic metachronism, for the same cilia beat cycle when the wavespeed is increased such that inertial effects occur. Based on a parameter study, the net transport in the channel is described by a power-law relation of the amplitude, length and speed of the metachronal wave. It is found that the wavelength has the strongest effect on the viscosity-dominated fluid transport.","microfluidics; propulsion","en","journal article","Cambridge University Press","","","","","","","2012-08-30","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:bbd6366f-f452-4f24-b146-eb5249624232","http://resolver.tudelft.nl/uuid:bbd6366f-f452-4f24-b146-eb5249624232","Numerical Simulation of Turbulent Flow in Concentric Annuli","Boersma, B.J.; Breugem, W.P.","","2010","In this paper we consider a fully developed turbulent flow in a round pipe with a small inner annulus. The diameter of the inner annulus is less than 10% of the diameter of the outer pipe. As a consequence, the surface area of the inner pipe compared to the outer pipe is small. The friction exerted by the wall on the flow is proportional to the surface area and the wall shear stress. Due to the small surface area of the inner annulus the additional stress on the flow due to the presence of the annulus may expected to be negligible. However, it will be shown that the inner annulus drastically changes the flow patterns and gives rise to unexpected scaling properties. In previous studies (Chung et al., Int J Heat Fluid Flow 23:426–440, 2002; Churchill and Chan, AIChE J 41:2513–2521, 1995) it was argued that radial position of the point of zero shear stress does not coincide with the radial location of the point of maximum axial velocity. In our direct numerical simulations we observe a coincidence of these points within the numerical accuracy of our model. It is shown that the velocity profile close to the inner annulus is logarithmic.","Turbulence; Pipe flow; DNS","en","journal article","Springer Verlag","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:d6379127-c85d-4fe5-b05f-63c5667f6a09","http://resolver.tudelft.nl/uuid:d6379127-c85d-4fe5-b05f-63c5667f6a09","Particle Sedimentation in Wall-Bounded Turbulent Flows","Cargnelutti, M.; Breugem, W.A.; Portela, L.M.; Mudde, R.F.; Uijttewaal, W.S.J.; Stelling, G.S.","","2006","In this work, a comparison between the results of point-particle direct numerical simulations and PIV/PTV experiments of a particle-laden horizontal channel flow is presented. The numerical simulations were preformed trying to mimic as much as possible the experimental conditions. The accuracy of the point-particle approach was evaluated by comparison of the concentration, velocity and velocity fluctuation profiles. The agreement was good, both qualitatively and quantitatively, in the central part of the channel. However, in the near-wall region some differences were found. This can be explained by the lack of resuspension present in the simulations, because we considered only the fluid-particle interaction (one-way coupling) and neglected both the particle-fluid interaction (two-way coupling) and the particle-particle interaction (collisions).","particle-laden flows; turbulence; DNS; PIV","en","conference paper","Delft University of Technology; European Community on Computational Methods in Applied Sciences (ECCOMAS)","","","","","","","","Applied Sciences","","","","",""
"uuid:2b90abcc-3488-41f4-b70e-f2afdd8c3a0e","http://resolver.tudelft.nl/uuid:2b90abcc-3488-41f4-b70e-f2afdd8c3a0e","Particle Sedimentation in Wall-Bounded Turbulent Flows","Cargnelutti, M.; Breugem, W.A.; Portela, L.M.; Mudde, R.F.; Uijttewaal, W.S.J.; Stelling, G.S.","","2006","In this work, a comparison between the results of point-particle direct numerical simulations and PIV/PTV experiments of a particle-laden horizontal channel flow is presented. The numerical simulations were preformed trying to mimic as much as possible the experimental conditions. The accuracy of the point-particle approach was evaluated by comparison of the concentration, velocity and velocity fluctuation profiles. The agreement was good, both qualitatively and quantitatively, in the central part of the channel. However, in the near-wall region some differences were found. This can be explained by the lack of resuspension present in the simulations, because we considered only the fluid-particle interaction (one-way coupling) and neglected both the particle-fluid interaction (two-way coupling) and the particle-particle interaction (collisions).","particle-laden flows; turbulence; DNS; PIV","en","conference paper","","","","","","","","","","","","","",""
"uuid:340510ef-9943-47ab-8bca-2ab78fd202ed","http://resolver.tudelft.nl/uuid:340510ef-9943-47ab-8bca-2ab78fd202ed","An Immersed Boundary Method for flows around rectangular objects","Breugem, W.P.","","2006","A second-order accurate and highly efficient Immersed Boundary Method (IBM) is presented for simulating flows along rectangular non-moving solid objects. In this method a rectangular object is placed on a staggered Cartesian grid such that its boundary coincides with grid points for the boundary-normal velocity component. By imposing forces at the grid points nearest to and on the boundary, the no-slip condition for the boundary-parallel velocity components issatisfied exactly, while the no-penetration condition for the boundary-normal velocity component is satisfied to a very good approximation. The accuracy of the IBM requires a pressure-correction method in which the correction pressure is small, which is accomplished by adding a fraction of the correction pressure to the pressure after every time step. It is shown that for the currently used second-order Adams-Bashforth scheme this fraction must not exceed one for maintaining stability. Furthermore, a von Neumann stability analysis has been performed, from which it is argued that the forces imposed in the IBM will usually not affect the numerical stability. The method has been successfully applied to both laminar and turbulent flows through a porous medium consisting of a periodic three-dimensional regular array of cubes.","Immersed Boundary Method; pressure-correction method; von Neumann stability analysis; porous medium","en","conference paper","","","","","","","","","","","","","",""
"uuid:f8dcbbe4-327a-4061-a318-4f0e9c667f9e","http://resolver.tudelft.nl/uuid:f8dcbbe4-327a-4061-a318-4f0e9c667f9e","The influence of wall permeability on turbulent channel flow","Breugem, W.P.; Boersma, B.J.; Uittenbogaard, R.E.","","2006","","","en","journal article","Cambridge University Press","","","","","","","","Mechanical, Maritime and Materials Engineering","","","","",""
"uuid:8f40233e-c326-4e60-8f18-09df59b88f47","http://resolver.tudelft.nl/uuid:8f40233e-c326-4e60-8f18-09df59b88f47","The influence of wall permeability on laminar and turbulent flows: Theory and simulations","Breugem, W.P.","Nieuwstadt, F.T.M. (promotor); Boersma, B.J. (promotor)","2005","The study of flows over permeable walls is relevant to many applications. Examples are flows over and through porous river beds, vegetation, snow, heat exchangers of foam metal, and oil wells. The main objectives of this thesis are to gain insight in the influence of wall permeability on both laminar and turbulent flows, and to develop a formalism for Direct Numerical Simulations (DNS) of turbulent flows over permeable walls. To describe flow inside a permeable wall, we use the Volume--Averaged Navier--Stokes (VANS) equations for the volume--averaged flow. The latter is defined as a weighted volume average of the microscopic flow, and is continuous throughout the porous medium. To solve the VANS equations, closures are needed for the subfilter--scale stress and the drag force. The latter is investigated in more detail in chapter 4. In chapter 3, an analysis is given of the influence of wall permeability on the laminar boundary layer over a wedge. A generalized Falkner--Skan equation is derived. Results are shown for various wedge angles. In chapter 5, a formalism is developed for DNS of turbulent flow in a plane channel with a permeable bottom wall. The VANS equations are used to simulate the flow inside the permeable wall. Results are shown from four simulations, for which only the wall porosity was changed. The influence of wall permeability can be characterized by the permeability Reynolds number. Turbulence near a highly permeable wall is dominated by relatively large vortical structures, which originate possibly from a Kelvin--Helmholtz type of instability. These structures cause an exchange of momentum between the channel and the permeable wall and consequently the skin friction increases. In chapter 6, the formalism developed in chapter 5 is validated. A DNS has been performed of turbulent channel flow over a permeable wall consisting of a Cartesian grid of 30x20x9 cubes. An Immersed Boundary Method is used to enforce a zero velocity on the cubes. The results of the DNS compares very well with a second DNS in which the VANS equations are used for the flow inside the permeable wall.","permeable / porous and rough; laminar and turbulent flows; volume averaging; boundary layer and falkner-skan; direct numerical simulations (dns); immersed boundary method (ibm)","en","doctoral thesis","","","","","","","","","Mechanical, Maritime and Materials Engineering","","","","",""
"uuid:ebfe6cc9-0251-4990-88a4-fd0410d5223b","http://resolver.tudelft.nl/uuid:ebfe6cc9-0251-4990-88a4-fd0410d5223b","Direct numerical simulations of turbulent flow over a permeable wall using a direct and a continuum approach","Breugem, W.P.; Boersma, B.J.","","2005","A direct numerical simulation (DNS) has been performed of turbulent channel flow over a three-dimensional Cartesian grid of 30×20×9 cubes in, respectively, the streamwise, spanwise, and wall-normal direction. The grid of cubes mimics a permeable wall with a porosity of 0.875. The flow field is resolved with 600×400×400 mesh points. To enforce the no-slip and no-penetration conditions on the cubes, an immersed boundary method is used. The results of the DNS are compared with a second DNS in which a continuum approach is used to model the flow through the grid of cubes. The continuum approach is based on the volume-averaged Navier–Stokes (VANS) equations [ S. Whitaker, “The Forchheimer equation: a theoretical development,” Transp. Porous Media 25, 27 (1996) ] for the volume-averaged flow field. This method has the advantage that it requires less computational power than the direct simulation of the flow through the grid of cubes. More in general, for complex porous media one is usually forced to use the VANS equations, because a direct simulation would not be possible with present-day computer facilities. A disadvantage of the continuum approach is that in order to solve the VANS equations, closures are needed for the drag force and the subfilter-scale stress. For porous media, the latter can often be neglected. In the present work, a relation for the drag force is adopted based on the Irmay [ “Modèles théoriques d’écoulement dans les corps poreux,” Bulletin Rilem 29, 37 (1965) ] and the Burke–Plummer model [ R. B. Bird, W. E. Stewart, and E. N. Lightfoot, Transport Phenomena (Wiley, New York, 2002) ], with the model coefficients determined from simulations reported by W. P. Breugem, B. J. Boersma, and R. E. Uittenbogaard [“Direct numerical simulation of plane channel flow over a 3D Cartesian grid of cubes,” Proceedings of the Second International Conference on Applications of Porous Media, edited by A. H. Reis and A. F. Miguel (Évora Geophysics Center, Évora, 2004), p. 27 ]. The results of the DNS with the grid of cubes and the second DNS in which the continuum approach is used, agree very well.","channel flow; flow through porous media; porosity; drag; flow simulation; Navier-Stokes equations; shear turbulence","en","journal article","American Institute of Physics","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""
"uuid:35f85715-4a25-47e2-bcd0-4ad00e3958f0","http://resolver.tudelft.nl/uuid:35f85715-4a25-47e2-bcd0-4ad00e3958f0","Recovery of Carbon Monoxide and Hydrogen from Low Joule Gas followed by reaction with Ethylene","Breugem, A.J.; Gerritsma, L.J.; Krul, R.A.; Over, M.J.J.","","2001","Document(en) uit de collectie Chemische Procestechnologie","","en","report","Delft University of Technology","","","","","","","","Applied Sciences","DelftChemTech","","","",""
"uuid:009b9f8c-07f5-446f-aa13-b31ed1fee36e","http://resolver.tudelft.nl/uuid:009b9f8c-07f5-446f-aa13-b31ed1fee36e","Some issues related to the stress IB method for flow around rectangular obstacles","Breugem, W.P.; Pourquie, M.; Boersma, B.J.","","","The Immersed Boundary Method (IBM) is a powerful method for simulating flows in complex geometries [1,2]. In this method complex geometries are embedded on a computational grid, which usually does not conform to the shape of the geometries. No boundary conditions are specified, but instead in the vicinity of solid boundaries forces are imposed on the flow to enforce the no-slip and no-penetration conditions. As compared to methods using a body-fitted grid, the advantages of the IBM are the computational efficiency (in particular when using a simple Cartesian grid), the ability to represent moving obstacles without the need for regridding and the relative ease of programming. However, disadvantages of the IBM are that it requires typically more grid points to represent the flow near solid boundaries and there may be non-zero slip and penetration velocities across solid boundaries.","","en","conference paper","","","","","","","","","Mechanical, Maritime and Materials Engineering","Process and Energy","","","",""