Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session LP: Turbulence Simulations: LES III |
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Chair: Fernando Grinstein, Los Alamos National Laboratory Room: Hilton Chicago Stevens 1 |
Tuesday, November 22, 2005 8:00AM - 8:13AM |
LP.00001: Numerical Study of Flow Over Two Circular Cylinders Arranged in Tandem at High Reynolds Numbers using Large Eddy Simulation Raymond Cohen, Andrew Ooi, Gianluca Iaccarino, Frank Ham Previously published exprimental data of the flow around two circular cylinders arranged in tandem have shown that for small spacings between the cylinders, the shear layer from the upstream cylinder reattaches to the downstream cylinder, hence creating a recirculation region in between the two cylinders. The experimental data was obtained at Re=65,000 and it was found that beyond a critical spacing (L/D $\sim $ 4.0), the upstream shear layer ceases to attach to the downstream cylinder, resulting in a dramatic change in the flow mechanisms. Previous numerical studies using two-dimensional RANS and URANS were unsatisfactory at predicting the length of the recirculation region of the upstream cylinder and consequently badly predicted the hydrodynamic forces between the two cylinders. In this study, Large Eddy Simulation with a dynamic Smagorinsky subgrid-scale model was used to investigate the flow around two circular cylinders arranged in tandem. Results from high Reynolds numbers simulations will be presented and practical considerations in using LES in such a flow configuration will be discussed. [Preview Abstract] |
Tuesday, November 22, 2005 8:13AM - 8:26AM |
LP.00002: Implementation of the Velocity-Scalar Filtered Mass Density Function for Large Eddy Simulation of Turbulent Reacting Flows Reza Sheikhi, Peyman Givi, Stephen Pope Our recently developed methodology ``velocity-scalar filtered mass density function'' (VSFMDF) is implemented for large eddy simulation (LES) of variable density, turbulent reacting flows. The VSFMDF represents the joint velocity-scalar probability density function of the subgrid scale quantities and is obtained by solving its modeled transport equation. In this equation, the effects of convection and chemical reaction appear in closed forms. The unclosed terms are modeled in a fashion similar to PDF methods [1]. This is the most general form of the filtered density function method for reacting flow simulations. The modeled VSFMDF transport equation is solved by a Lagrangian Monte Carlo method. The methodology is employed to simulate turbulent shear flows. The predicted results are assessed by comparisons with data generated by direct numerical simulation (DNS) and with experimental measurements. The VSFMDF results show a close agreement with DNS. The results also agree favorably with laboratory data and demonstrate several of the features observed experimentally.\newline \newline [1] Pope, S. B., Turbulent flows, Cambridge University Press, Cambridge, UK (2000). [Preview Abstract] |
Tuesday, November 22, 2005 8:26AM - 8:39AM |
LP.00003: The Critical Importance of Aliasing in Near-Surface Large-Eddy Simulation Tie Wei, James Brasseur Because large-eddy simulation (LES) implies unresolved energy, nonlinear aliasing is always of concern. However, aliasing may be critically detrimental to LES accuracy near surfaces and other regions where integral scales become badly under-resolved. We therefore carried out \textit{a priori} analyses of aliasing in progressively under-resolved LES using DNS of homogeneous shear-driven turbulence. The spectral form of the aliased terms is used to explain differences in aliasing level among advective, divergence, skew-symmetric and rotational forms. We find that greater kinetic energy in the unresolved scales implies greater aliasing. However, as integral scales become progressively under-resolved consistent with near-surface LES, aliasing in the nonlinear term increases rapidly to levels as high as 60{\%} the alias-free term! Shear-induced anisotropies alter the balance of aliasing among single/double/triple aliasing components and directions. It is therefore critically important to remove aliasing error near surfaces, but without additional loss of resolution, so grid shifting is preferred over truncation. We discuss grid-shifting methods relevant to under-resolved shear turbulence. [Preview Abstract] |
Tuesday, November 22, 2005 8:39AM - 8:52AM |
LP.00004: Subgrid scale models for large eddy simulations of a confined rectangular jet Anup Gokarn, Francine Battaglia, Rodney Fox, James Hill Large eddy simulations are performed and compared with experimental data obtained for a liquid-phase turbulent flow in a rectangular duct. Three streams initially separated by two splitter plates enter the duct and mix, with the central stream having a higher velocity than the outer streams. All simulations are for water at a Reynolds number of 50,000 (based on hydraulic diameter and flow rate). The numerical formulation is based on the pressure Poisson equation and employs a sixth-order compact finite-difference scheme for the spatial derivatives and a third-order compact Runge-Kutta scheme for the time derivative on a partially-staggered variable arrangement. Four subgrid scale models are tested: the standard Smagorinsky model, the dynamic eddy viscosity model, the mixed model and the structure function model. Wall functions are also tested. One-point and two-point statistical correlations such as mean velocity, velocity fluctuations, Reynolds stresses, dissipation rate and the turbulent kinetic energy are compared against those obtained from the experiments. [Preview Abstract] |
Tuesday, November 22, 2005 8:52AM - 9:05AM |
LP.00005: Transition and Turbulence Decay in the Taylor-Green Vortex Fernando Grinstein, Dimitris Drikakis, Christer Fureby, David Youngs The Taylor-Green Vortex (TGV) is a fundamental case that has been traditionally used as prototype of vortex stretching and consequent production of small-scale eddies, to investigate the basic dynamics of transition to turbulence. As such, it is also a very convenient case in which to test the ability of explicit and implicit subgrid scale (SGS) modeling to simulate the basic laws of turbulence. We report on the performance of Monotone Integrated LES (MILES) in emulating the space/time development of transition to turbulence and self-similar decay in the TGV without resorting to an explicit SGS model. MILES based on various limiting algorithms, including Flux Corrected Transport, characteristics-based Godunov, Lagrange-Remap, and several other hybrid methods is tested and compared with a conventional (mixed) LES method combining one-equation eddy-viscosity and scale-similarity models. The agreement between MILES, mixed-model LES, and the previous DNS by Brachet et al. (1983) is quite good in estimating the time and height of the dissipation peak associated with the TGV inviscid instability. [Preview Abstract] |
Tuesday, November 22, 2005 9:05AM - 9:18AM |
LP.00006: Investigation of conditional subgrid-scale scalar flux and its production rate Qinglin Chen, Danhong Wang, Hengbin Zhang, Chenning Tong The effects of the subgrid-scale (SGS) velocity and scalar and SGS models on the resolvable-scale joint probability density function (JPDF) are studied. It is shown that the SGS turbulence evolve the JPDF though the conditional mean SGS stress and flux, their production rates, and the SGS scalar variance production rate. The mean SGS stress and scalar flux production rate are predicted using Lumley's assumption. Analyses using data obtained in a slightly heated turbulent jet show that the mean SGS stress, scalar flux, and their production rates have filter-scale dependences consistent with predictions, suggesting that the SGS turbulence has diminishing influence on the lower-order resolvable-scale statistics for inertial-range filter scales. The Smagorinsky model predictions also have similar filter-scale dependences, suggesting that the models have diminishing effects on lower-order LES statistics. The measured conditional SGS stress and SGS flux as well as the conditional production rates decrease much slower than the predicted filter dependences, indicating that the SGS turbulence has non-trivial effects on the high-order resolvable-scale statistics even for inertial-range filter scales. The Smagorinsky models predictions of these conditional statistics decrease slower with the filter scale than predictions but do not agree with measurements; therefore the models are likely to influence the high-order LES statistics but in ways different from that of the SGS turbulence. [Preview Abstract] |
Tuesday, November 22, 2005 9:18AM - 9:31AM |
LP.00007: Characterization of discrete commutative filters Andreas Haselbacher, Oleg Vasilyev Previous work by the authors (J. Comp. Phys., 187: 197-211, 2003) derived and analyzed discrete commutative filters. On uniform unbounded grids, the discrete commutation error was shown numerically to be of the order of the machine precision. On non-uniform and bounded grids, numerical experiments confirmed the theoretical prediction that the discrete commutation error depends on both the order of accuracy of the discrete filter operator and the order of accuracy of the spatial discretization. For discrete filters to be of genuine practical value, their widths must be prescribed. This leads to the problem of characterization of discrete filters, that is, how to express their width in terms of quantities such as the local grid spacing and filter moments. The presentation will describe ongoing investigations into the characterization of discrete filters. [Preview Abstract] |
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