Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session E12: Turbulence Simulation III |
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Chair: Robert Moser, University of Texas at Austin Room: 315 |
Sunday, November 20, 2011 4:40PM - 4:53PM |
E12.00001: Direct numerical simulation of stationary homogeneous stratified sheared turbulence Daniel Chung, Georgios Matheou Using direct numerical simulation (DNS), we investigate stationary and homogeneous driven turbulence in various stratifications, ranging from neutral to very stable. The Taylor Reynolds number is about 400, allowing an adequate separation of scales for the study of stratified turbulence dynamics. Analysis of the simulations is used to elucidate several aspects of stratified turbulence, including flux--gradient relations, length scales, spectra, the formation of layer, and criteria of turbulence collapse. [Preview Abstract] |
Sunday, November 20, 2011 4:53PM - 5:06PM |
E12.00002: High resolution DNS studies of long-time behavior of homogeneous turbulent shear flow Parvez Sukheswalla, T. Vaithianathan, Lance R. Collins As discussed in Isaza \& Collins [\emph{J. Fluid Mech.} {\bf 678}:14--40, 2011], the shear parameter $S^{*}$ has a pronounced effect on velocity gradient statistics for homogeneous turbulent shear flow (HTSF). Due to the importance of this effect, especially for higher $S^{*}$, we extended those studies to higher resolution using a new direct numerical simulation (DNS) code based on a pseudospectral algorithm that avoids remeshing [Brucker et al., \emph{J. Comp. Phys.} {\bf 225}:20--32, 2007], and decomposes the domain into ``pencils''. We present DNS with $2048\times 1024\times 1024$ grid points, achieving a maximum Taylor microscale Reynolds number of 300. The peak in the initial energy spectrum, viscosity, and box configuration also have been optimized to maximize the time window for well-resolved simulations (up to $S t=20$), ensuring we are well into the asymptotic regime. The DNS runs confirm the sensitivity of the large- and small-scale statistics to $S^{*}$, as was found by Isaza \& Collins. We also investigated the interaction between the fluctuating vorticity vector and rate-of-strain tensor as a function of scale, and find alignments vary dramatically, suggesting the primary source of enstrophy is at large scales, followed by a forward cascade to small scales. This helps explain the persistent sensitivity of the velocity gradient statistics to $S^{*}$. The combination of results suggests a new framework for modeling HTSF at high values of $S^{*}$. [Preview Abstract] |
Sunday, November 20, 2011 5:06PM - 5:19PM |
E12.00003: DNS investigation of late-stage transition in hypersonic channel flow Zhimin Xie, Sharath Girimaji We perform direct numerical simulations (DNS) of normal-mode evolution in hypersonic channel flows to investigate late-stage transition physics. A well-validated compressible flow solver based on Gas-Kinetic Method (GKM) is used in the computations. In this temporal DNS, periodic boundary condition is employed in the streamwise direction and wall conditions at the normal boundaries. The DNS code is first validated against analytical transition (Orr-Sommerfeld) results in the incompressible flow regime. In the compressible regime, the code is validated against homogeneous shear flow rapid distortion theory (RDT) data. Direct numerical simulation of normal modes in laminar channel flow at very high Mach number shows that the evolution exhibits a three-stage behavior similar to that observed in many hypersonic boundary layer experiments and RDT of homogeneous shear flow. The physics associated with each transition stage is investigated in great detail and a physical picture of late-stage transition is proposed. [Preview Abstract] |
Sunday, November 20, 2011 5:19PM - 5:32PM |
E12.00004: Study of high speed turbulent jets in crosslfow using numerical simulations Xiaochuan Chai, Krishnan Mahesh Numerical simulations are used to study a sonic jet injected into a supersonic crossflow and a supersonic jet injected into a subsonic crossflow, where the flow conditions are based on Santiago {\it et al.}'s (1997) and Beresh {\it et al.}'s (2005) experiments, respectively. A finite volume compressible Navier--Stokes solver on unstructured grids (Park \& Mahesh 2007) is used. The simulations successfully reproduce experimentally observed shock system and turbulent flow structures such as the jet shear layer vortices, wake vortices, horseshoe vortices that wrap up in front of the jet and the counter rotating vortex pair (CVP) downstream of the jet. The dynamics of these flow structures are discussed. The effects of grid resolution and crossflow boundary layer condition are studied, as well as the contribution of sub-grid scale model. The time averaged flow fields are compared to the experimental results, and reasonable agreement is observed. [Preview Abstract] |
Sunday, November 20, 2011 5:32PM - 5:45PM |
E12.00005: Lattice Boltzmann Simulations of Skin-Friction Drag Reduction in Turbulent Channel Flow with Slip/No Slip Wall Ridges Amirreza Rastegari, Rayhaneh Akhavan To gain a better understanding of the mechanisms at work in skin friction drag reduction with superhydrophobic surfaces, Lattice Boltzmann simulations were performed in turbulent channels with alternating slip/no slip ridges on the walls. Simulations were performed in turbulent channels of size $5h \times 2.5 \times 2h$ and $10h \times 5h \times 2h$ at a base Reynolds number of $Re_\tau \sim 230$. Alternating slip/no slip ridges of width $4 \le w+ \le 140$, aligned in the streamwise direction, all with the same fractional area of slip boundary, were studied. Drag reductions of 4\%, 8\%, 21\%, 33\% and 47\%, corresponding to slip velocities of $U_{slip}/U_{bulk}=$ 0.05, 0.1, 0.26, 0.31 and 0.36 were observed for $w+=g+=$ 4, 8, 40, 70 and 140, respectively. The mean velocity profiles display the characteristics of combined slip described by Min and Kim [Min et al. 2004]. The streamwise and spanwise turbulence intensities show large slips at the wall, the magnitude of which increases with increasing drag reduction. Examination of the anisotropy invariant maps shows a shift of turbulence structure towards the one-dimensional turbulence limit near the wall with increasing drag reduction. For $z^+ > 25$, the turbulence structure returns to the isotropic limit. [Preview Abstract] |
Sunday, November 20, 2011 5:45PM - 5:58PM |
E12.00006: High-resolution simulations of forced compressible isotropic turbulence Shriram Jagannathan, Diego Donzis Direct numerical simulations of compressible turbulent flows are several times more expensive than their incompressible counterparts. Therefore, using large computing resources efficiently is even more pressing when studying compressible turbulence. A highly scalable code is presented which is used to perform simulations aimed at understanding fundamental turbulent processes. The code, which is based on a 2D domain decomposition, is shown to scale well up to 128k cores. To attain a statistically stationary state a new scheme is developed which involves large-scale stochastic forcing (solenoidal or dilatational) and a procedure to keep mean internal energy constant. The resulting flows show characteristics consistent with results in the literature. The attainable Reynolds and turbulent Mach numbers for given computational resources depend on the number of grid points and the degree to which the smallest scales are resolved that are given by Kolmogorov scales. A systematic comparison of simulations at different resolutions suggests that the resolution needed depends on the particular statistic being considered. The resulting database is used to investigate small-scale universality, the scaling of spectra of velocity, density and temperature fields, structure functions and the trends towards high-Reynolds number asymptotes. Differences with incompressible results are highlighted. [Preview Abstract] |
Sunday, November 20, 2011 5:58PM - 6:11PM |
E12.00007: Interaction of a converging shock wave with isotropic turbulence Ankit Bhagatwala, Sanjiva Lele Simulations of converging spherical shock waves propagating through a region of compressible isotropic turbulence (Taylor scale Re = 100, Mt = 0.6) are carried out. Parametric variation with respect to initial shock Mach number is studied. Both converging and reflected phases of the shock are studied. Vorticity and turbulent kinetic energy are amplified due to passage of the shock. The vorticity-dilatation term is primarily responsible for the observed behavior. This is confirmed through Eulerian and Lagrangian statistics. Transverse vorticity amplification is compared with linear planar shock turbulence theory. The smallest eddies, represented by the Kolmogorov scale, decrease in size after passing through the converging shock. Distortion of the shock due to turbulence is also investigated and quantified. Turbulence also affects maximum compression achieved at the point of shock reflection, when the shock radius is at a minimum. [Preview Abstract] |
Sunday, November 20, 2011 6:11PM - 6:24PM |
E12.00008: Lagrangian motions and distribution of particles in strained turbulence Chung-min Lee, Prasad Perlekar, Federico Toschi, Armann Gylfason Direct numerical simulation is employed to study the influence of straining on the motions of passive and inertial particles in turbulent flows. Our focus is on parametric dependencies of particle distribution statistics, as well as Lagrangian velocity and acceleration statistics. Results are compared with our new experimental data, as well as existing numerical and experimental data. Our numerical algorithm is based on the Rogallo method and simulates the flow field in a non-cubical, deforming domain and our particle advancing scheme assumes one-way coupling between the flow field and the particle field and is specifically adapted to the present flow geometry. [Preview Abstract] |
Sunday, November 20, 2011 6:24PM - 6:37PM |
E12.00009: Solenoidal Synthetic Turbulent Velocity Field for LES Inflow and Initial Conditions Adrian Sescu, Ray Hixon, Charles Meneveau Current numerical techniques for the prediction of realistic turbulent flows require turbulent inflow or/and initial conditions that at least must match a given set of statistics and satisfy the divergence-free condition. These techniques are increasingly coupled with aeroacoustic calculations wherein the propagation of acoustic waves has to be accurately captured, as opposed to traditional CFD methods where the acoustic waves are simply damped out. This work proposes a method to generate a divergence-free turbulent velocity field based on the assumption that turbulence can be considered as a summation of random eddies satisfying specific statistics. The streamfunction concept and the requirement that the individual eddies must satisfy the linearized momentum equations about the mean flow are used to enforce the divergence-free condition. Experimental benchmark data for spatially decaying turbulence and nonhomogeneous rotor-wake turbulence from NASA's Fan Source Diagnostic Test are used to evaluate the proposed synthetic eddy method. [Preview Abstract] |
Sunday, November 20, 2011 6:37PM - 6:50PM |
E12.00010: Direct Numerical Simulation of Stationary Homogeneous Variable-Density Turbulence Jaiyoung Ryu, Daniel Livescu The turbulence characteristics in statistically stationary turbulent flows composed of two incompressible miscible fluids with different densities are studied using Direct Numerical Simulations (DNS). When the two fluids have very different densities, the differential inertial effects lead to active scalar behavior. To distinguish this from the Boussinesq case, when the two fluids have commensurate densities, we call the former variable-density flows. In order to achieve a statistically stationary state, the velocity field is forced in the real space, using a linear forcing mechanism, while the active scalar field is de-mixed at a rate counteracting the normal diffusion processes using a real-space forcing based on a chemical reaction analogy. The active scalar influence on the turbulence characteristics are discussed as well as the ratios of turbulence to scalar scales for different Atwood, Schmidt, and Reynolds numbers and forcing properties. Finally, the decay of variable-density turbulence from various stationary states is also studied. [Preview Abstract] |
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