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Energy Cascade Phenomena in Temporal Boundary Layers

Cimarelli, Andrea (author), Boga, Gabriele (author), Pavan, Anna (author), Costa, Pedro (author), Stalio, Enrico (author)

The geometrically complex mechanisms of energy transfer in the compound space of scales and positions of wall turbulent flows are investigated in a temporally evolving boundary layer. The phenomena consist of spatially ascending reverse and forward cascades from the small production scales of the buffer layer to the small dissipative scales...

journal article 2023

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Experimental and numerical investigation into the drag performance of dimpled surfaces in a turbulent boundary layer

van Campenhout, O.W.G. (author), van Nesselrooij, M. (author), Lin, Y. (author), Casacuberta Puig, J. (author), van Oudheusden, B.W. (author), Hickel, S. (author)

Although several previous studies have reported a potential drag-reducing effect of dimpled surfaces in turbulent boundary layers, there is a lack of replicability across experiments performed by different research groups. To contribute to the dialogue, we scrutinize one of the most studied dimple geometries reported in the literature, which...

journal article 2023

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Experimental Investigation into the Drag Performance of Chevron-Shaped Protrusions in Wall-Bounded Turbulence

Carrasco Grau, J. (author), van Campenhout, O.W.G. (author), Hartog, F.H. (author), van Nesselrooij, M. (author), Baars, W.J. (author), Schrijer, F.F.J. (author)

Chevron-shaped protrusions have been proposed in the literature for turbulent skin friction reduction. However, there is no consensus on the performance of this passive flow control technique; both an increase and a decrease in drag have been observed in previous studies. There is also no experimental evidence to support the working mechanism...

journal article 2023

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Direct numerical simulation of one-sided forced thermal convection in plane channels

Pirozzoli, Sergio (author), Modesti, D. (author)

We carry out direct numerical simulations (DNS) of turbulent flow and heat transfer in pressure-driven plane channels, by considering cases with heating on both walls, as well as asymmetric heating limited to one of the channel walls. Friction Reynolds numbers up to are considered, and Prandtl numbers from to, the temperature field being...

journal article 2023

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Microphones as Airspeed Sensors for Unmanned Aerial Vehicles

Makaveev, M.K. (author), Snellen, M. (author), Smeur, E.J.J. (author)

This paper puts forward a novel design for an airspeed instrument aimed at small fixed-wing tail-sitter unmanned aerial vehicles. The working principle is to relate the power spectra of the wall-pressure fluctuations beneath the turbulent boundary layer present over the vehicle’s body in flight to its airspeed. The instrument consists of two...

journal article 2023

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Direct numerical simulation of supersonic turbulent flows over rough surfaces

Modesti, D. (author), Sathyanarayana, Srikanth (author), Salvadore, Francesco (author), Bernardini, Matteo (author)

We perform direct numerical simulation of supersonic turbulent channel flow over cubical roughness elements, spanning bulk Mach numbers -, both in the transitional and fully rough regime. We propose a novel definition of roughness Reynolds number which is able to account for the viscosity variations at the roughness crest and should be used...

journal article 2022

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Reducing turbulent convective heat transfer with streamwise plasma vortex generators

Castellanos, Rodrigo (author), Michelis, Theodorus (author), Discetti, Stefano (author), Ianiro, Andrea (author), Kotsonis, M. (author)

The effect of streamwise plasma vortex generators on the convective heat transfer of a turbulent boundary layer is experimentally investigated. A Dielectric Barrier Discharge (DBD) plasma-actuator array is employed to promote pairs of counter-rotating, streamwise-aligned vortices embedded in a well-behaved turbulent boundary layer over a flat...

journal article 2022

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An alternative permeable topology design space for trailing-edge noise attenuation

Luesutthiviboon, S. (author), Ragni, D. (author), Avallone, F. (author), Snellen, M. (author)

This study focuses upon a new permeable topology design concept as an alternative to porous metal foams, for turbulent boundary layer trailing-edge (TBL-TE) noise attenuation. The present permeable topology has unconventional characteristics with respect to the metal foams: a combination of low flow resistivity r and high form drag...

journal article 2021

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Do coherent structures organize scalar mixing in a turbulent boundary layer?

Eisma, H.E. (author), Westerweel, J. (author), van de Water, W. (author)

A scalar emanating from a point source in a turbulent boundary layer does not mix homogeneously, but is organized in large regions with little variation of the concentration: uniform concentration zones. We measure scalar concentration using laser-induced fluorescence and, simultaneously, the three-dimensional velocity field using tomographic...

journal article 2021

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Temporal characteristics of the probability density function of velocity in wall-bounded turbulent flows

Laskari, A. (author), McKeon, Beverley J. (author)

The probability density function (p.d.f.) of the streamwise velocity has been shown to indicate the presence of uniform momentum zones in wall-bounded turbulent flows. Most studies on the topic have focused on the instantaneous characteristics of this p.d.f. In this work, we show how the use of time-resolved particle image velocimetry data...

journal article 2021

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Dispersive stresses in turbulent flow over riblets

Modesti, D. (author), Endrikat, Sebastian (author), Hutchins, Nicholas (author), Chung, Daniel (author)

We carry out direct numerical simulations of turbulent flow over riblets, streamwise- aligned grooves that are designed to reduce drag by modifying the near-wall flow. Twenty riblet geometries and sizes are considered, namely symmetric triangular with tip angle, and, asymmetric triangular, blade and trapezoidal. To save on computational cost,...

journal article 2021

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Near wall coherence in wall-bounded flows and implications for flow control

Samie, M. (author), Baars, W.J. (author), Rouhi, A. (author), Schlatter, P. (author), Örlü, R. (author), Marusic, I. (author), Hutchins, N. (author)

Opposition-control of the energetic cycle of near wall streaks in wall-bounded turbulence, using numerical approaches, has shown promise for drag reduction. For practical implementation, real-time opposition control is only realizable if there is a degree of coherence between the turbulent velocities passing a sensor and the target point...

journal article 2020

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Effect of drag reducing riblet surface on coherent structure in turbulent boundary layer

CUI, Guangyao (author), PAN, C. (author), WU, Di (author), Ye, Q. (author), WANG, Jinjun (author)

The characteristics of turbulent boundary layer over streamwise aligned drag reducing riblet surface under zero-pressure gradient are investigated using particle image velocimetry. The formation and distribution of large-scale coherent structures and their effect on momentum partition are analyzed using two-point correlation and probability...

journal article 2019

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Temperature-activated change of permeable material properties for low-noise trailing edge applications

Mayer, Jonathan (author), Rubio Carpio, A. (author), Ragni, D. (author)

The present work analyses broadband noise scattering from permeable trailing edges with identical micro-structure but under a change of temperature. Experiments are performed in an anechoic wind tunnel using a NACA0018 airfoil at chord-based Reynolds numbers between 1.88 × 10⁵ and 3.14 × 10⁵ and no incidence. A...

journal article 2019

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Scaling and modelling of turbulence in variable property channel flows

Pecnik, Rene (author), Patel, A. (author)

We derive an alternative formulation of the turbulent kinetic energy equation for flows with strong near-wall density and viscosity gradients. The derivation is based on a scaling transformation of the Navier-Stokes equations using semi-local quantities. A budget analysis of the semi-locally scaled turbulent kinetic energy equation shows that...

journal article 2017

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Benefits of curved serrations on broadband trailing-edge noise reduction

Avallone, F. (author), van der Velden, W.C.P. (author), Ragni, D. (author)

Far-field noise and flow field over a novel curved trailing-edge serration (named as iron-shaped serration) are investigated. Spectra of the far-field broadband noise, directivity plots and the flow-field over the iron-shaped serration are obtained from numerical computations performed using a compressible Lattice-Boltzmann solver. The new...

journal article 2017

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Turbulent structure of high-amplitude pressure peaks within the turbulent boundary layer

Ghaemi, S. (author), Scarano, F. (author)

journal article 2013

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Turbulent drag reduction using fluid spheres

Gillissen, J.J.J. (author)

Using direct numerical simulations of turbulent Couette flow, we predict drag reduction in suspensions of neutrally buoyant fluid spheres, of diameter larger than the Kolmogorov length scale. The velocity fluctuations are enhanced in the streamwise direction, and reduced in the cross-stream directions, which is similar to the more studied case...

journal article 2013

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Tracking of vortices in a turbulent boundary layer

Elsinga, G.E. (author), Poelma, C. (author), Schröder, A. (author), Geisler, R. (author), Scarano, F. (author), Westerweel, J. (author)

journal article 2012

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Counter-hairpin vortices in the turbulent wake of a sharp trailing edge

Ghaemi, S. (author), Scarano, F. (author)

journal article 2011