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Since direct simulations of the incompressible Navier-Stokes equations are limited to relatively low-Reynolds numbers, dynamically less complex mathematical formulations are necessary for coarse-grain simulations. Eddy-viscosity models for Large-Eddy Simulation is probably the most popular example thereof: they rely on differential operators...
conference paper 2015
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High area ratio rocket engines generate strong vibro-acoustic loads primarily during transient operations, like start-up and shut-down of the engine. These loads can adversely affect the launch vehicle and its payload. Thus, an accurate prediction of the loads produced during engine start-up is pertinent to the safety and reliability of the...
conference paper 2015
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With transient LES and DNS simulations, we investigate flow in melt pools driven by thermocapillary forces. The developing pool is at first axisymmetric as are the boundary conditions, but flow instabilities arise that lead to 3D oscillatory flow patterns. At higher laser powers a sign-change in the surface tension temperature coefficient occurs...
conference paper 2015
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The demand of development and application of computational aeroacoustic (CAA) prediction tools for turbulence related noise is increasing to overcome the future requirements of low noise design. Fast and accurate prediction methods are necessary to be integrated into early design processes. Several numerical and experimental studies show that...
conference paper 2015
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Many technological applications are characterized by turbulent bounded flows with dispersed particles. For high mass load (particle/fluid mass ratio) a significant inter-phase momentum exchange occurs (two-way coupling regime), inducing a significant alteration of the turbulent field which, in turn, modifies the dynamics of the suspended phase....
conference paper 2015
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The result of a particle-image velocimetry (PIV) measurement is a velocity field averaged over interrogation windows. This severely affects the measurement of small-scale turbulence quantities when the interrogation window size is much larger than the smallest length scale in turbulence. A direct measurement of the dissipation rate demands the...
conference paper 2015
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Small aerosols drift down temperature or turbulence gradient since faster particles fly longer distances before equilibration. That fundamental phenomenon, called thermophoresis or turbophoresis, is widely encountered in nature and used in industry. It is universally believed that particles moving down the kinetic energy gradient must...
conference paper 2015
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Near the onset to turbulence in pipes, around Re = 1700-2000, turbulent puffs decay either directly or, at higher Reynolds numbers through splitting, with characteristic time-scales that exhibit a super-exponential dependence on Reynolds number [3, 1, 7]. The goal of our work [5] is to understand the phenomenology of this transition in terms of...
conference paper 2015
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Accurate simulation of turbulence remains one of the most challenging problems in nuclear reactor analysis and design. Due to limitations in computing resources, Reynolds averaged Navier Stokes models (RANS) continue to play an important role in reactor simulations. The Consortium for advanced simulations of light water reactors (CASL) is a...
conference paper 2015
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We examine the geometric orientation of the subfilter-scale scalar-flux vector in homogeneous isotropic turbulence. Vector orientation is determined using the eigenframe of the resolved strain-rate tensor. The Schmidt number is kept sufficiently large so as to leave the velocity field, and hence, the strain-rate tensor, unaltered by filtering in...
conference paper 2015
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The behavior of particles in compressible turbulence has been seldom investigated to date despite its importance in many natural and industrial flows. Direct numerical simulations of particle-laden compressible isotropic turbulence are performed to study the preferential concentration of particles and the underling mechanisms. It turns out that...
conference paper 2015
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A three-dimensional particle tracking velocimetry (3D-PTV) method was applied to study in details the single-particle resuspension (lift-off) events of large spherical particles. In order to increase statistics, we have utilized a wall-normal, tornado-like vortex that lifted the particles from surfaces of different roughness. Analyzing the three...
conference paper 2015
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The Direct Numerical Simulation (DNS) of an incompressible open channel flow over a layer of rigid spherical roughness elements fixed on the wall in well-packed square arrangement has been performed which shows values of the Reynolds number Rb ~ 6900 (ks+ ~ 100) and produces a mean velocity defect ∆U+ ~ 7 in the range of the fully-rough regime....
conference paper 2015
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This talk discusses the effects of a rigid solid boundary impeding the evolution of the Rayleigh-Taylor (RT) instability. The introduction of an obstacle completely alters the evolution of RT growth, instead of mixing the domain rapidly, a quasi-steady flow, rich in dynamics is established for long periods of time. Using a combination of low...
conference paper 2015
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We report a Direct Numerical Simulation (DNS) of turbulent Rayleigh-Bénard convection in a laterally unbounded domain confined between two horizontal parallel walls, for Rayleigh number 10^5 and Prandtl number 0.7. The DNS data are used to study the properties of the subgrid-scale flux of the active temperature field in the framework of Large...
conference paper 2015
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Modeling of heavy particles motion in turbulent flows still represents a challenge in engineering applications at high Reynolds number. Various techniques have arisen for describing such mono-dispersed solid phases with statistical methods. Some of those techniques relies on the assumption of using a velocity field to describe the particles...
conference paper 2015
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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...
conference paper 2015
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We will present the results of our recent numerical work on the nature of the phase diagram of turbulent Taylor-Couette (TC) flow, both with co- and counterrotating cylinder. The work can be seen as the extension of the famous experimental Andereck et al. phase diagram for Taylor-Couette flow just above the onset of instabilities, towards the...
conference paper 2015
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We propose the asymptotic theory of unsteady accumulation of inertial particles in the viscous sublayer of wall-bounded turbulent flow. We derive the diffusion equation for the particle concentration in the viscous sublayer and find the self-similar exact solution of this equation at large times. It is shown that near the wall the maximal...
conference paper 2015
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Large particles ($D \gg \eta$) immersed in a closed turbulent flow tend to explore in a non-uniformly way the cavity in which they are placed. Here we study the slow dynamics of large particles (with various size) advected in closed turbulent flows at different Reynolds numbers. We investigate the spatial sampling experienced by large particles...
conference paper 2015
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