Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session MD: Turbulence Simulations IV |
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Chair: Kelly Knight, Bechtel Corporation Room: Long Beach Convention Center 102B |
Tuesday, November 23, 2010 8:00AM - 8:13AM |
MD.00001: LES one-way coupling of nested grids using scale similarity model Kojiro Nozawa, Tetsuro Tamura The method for coupling between nested grids with turbulence energy smoothly transferred is proposed for LES turbulent flows. In this method fluctuating velocity simulated in a coarse grid is imposed to a fine grid. As a result, time-sequential data of the grid-scale velocity fluctuation of the fine grid can be obtained utilizing the scale similarity concept [J. Bardina, J. H. Ferziger and W. C. Reynolds, AIAA Paper, No.80-1357, (1980)]. The a-priori test of a turbulent boundary layer flow over a rough surface is conducted to validate this method. In order to fulfill simulations of spatially developing turbulent boundary layer flows we apply the quasi-periodic boundary condition to the streamwise direction [K. Nozawa and T. Tamura, Proc. of the Turbulent Shear Flow Phenomena, vol.2, 443-448.(2001)]. In the test coarsely resolved velocity data which is generated filtering finely resolved LES data are applied for directly reproducing subgrid-scale components of the coarsely resolved LES. The reproduced fluctuation velocity agrees well with the true value which can be derived by subtracting the generated coarsely resolved velocity data from the finely resolved LES data. Also, the spectra of the reproduced streamwise fluctuation velocities at higher wave number range corresponding to the fine mesh size fit to the -5/3 power law for the inertial subrange. This method is expected to appropriately combine the meso-scale meteorological model with the LES model of urban scale. [Preview Abstract] |
Tuesday, November 23, 2010 8:13AM - 8:26AM |
MD.00002: Formulation of smoothed-particle hydrodynamics method for turbulent free-surfaceflows Akihiko Nakayama, Hiroshi Inokuma, Kenta Ikenaga The Smoothed Particle Hydrodynamics (SPH) method is proving useful to compute various flows involving large deformation of flow field such as wave breaking and motion of solid bodies in fluids. The effects of turbulent fluctuations that are important in most large-scale flows in engineering and environmental applications have not been studied to the extent and the degree at which conventional simulation methods like Large Eddy Simulation (LES) have been studied. We try to formulate the method as filtering in the moving frame of reference and identify what are exactly the effects of turbulent fluctuations that are not resolved by this smoothed particle representation and show a method of modeling the effects. A few examples of numerical calculation results are presented to show the effectiveness of the proposed formulation. [Preview Abstract] |
Tuesday, November 23, 2010 8:26AM - 8:39AM |
MD.00003: Turbulent modeling for low speed compressible flow ChungGang Li, J.A. Domaradzki, WuShung Fu An investigation of turbulence models at high Reynolds numbers is conducted. The numerical code uses the Roe scheme and preconditioning matrix and dual time stepping are adopted for economizing the computational time and improving convergence properties. In order to validate the code, DNS of the turbulent channel flow are performed at Reynolds numbers, based on the friction velocity, of 180 and 500. The results for the mean velocity profiles and turbulent intensities are in good agreement with the benchmark DNS data obtained by spectral codes. The same code is used to perform LES with different models, among them the classical Smagorinsky model and the Truncated Navier Stokes (TNS) method, and comparisons are made with databases for high friction velocity Reynolds numbers of 1000 and 2000. [Preview Abstract] |
Tuesday, November 23, 2010 8:39AM - 8:52AM |
MD.00004: Numerical computations of turbulent flows; LES/SAS comparison Marcel Ilie, Stefan Llewellyn Smith In aerodynamics, the unsteady fluctuations of the flow field can have a significant influence on stalled flow characteristics, or on the forces acting on different parts of the aircraft. In non-aerodynamic flows, there is a multitude of mixing problems such as piston engines or turbine blade cooling where steady Reynolds-Averaged Navier-Stokes (RANS) solutions are not adequate. On the other hand the unsteady Reynolds-Averaged Navier-Stokes (URANS) has proven to be insufficient. This is due to the highly dissipative nature of standard URANS. The use of Large Eddy Simulation (LES) methods is often not practical, due to the requirement of very fine grid resolution near walls. Direct Numerical Simulations (DNS) compute the flow field without further simplifications. However, due to a wide range of length and time scales present in turbulent flows, the use of DNS is still limited to low-Reynolds-number flows and relatively simple geometries. To combine the advantages of a URANS with the higher resolution of a LES, hybrid methods such as Detached Eddy Simulation (DES) or Scale Adaptive Simulation (SAS) are preferred. The present research concerns the suitability of SAS for the computation of highly separated flows. The results show that SAS is a promising approach for the computation of massively separated flows. [Preview Abstract] |
Tuesday, November 23, 2010 8:52AM - 9:05AM |
MD.00005: Wall-modeling for large-eddy simulation of high Reynolds number supersonic flows Soshi Kawai, Johan Larsson, Sanjiva Lele We present an idea of approximate wall-boundary-condition approach with dynamic procedure for large-eddy simulation of Mach 3 supersonic turbulent boundary layer at various Reynolds numbers ($Re_{\delta}=2 \times 10^4$, $10^5$ and $10^6$) on a flat plate. This wall-model is the extension of previous work by Wang and Moin [Phys. Fluid, \textbf{14}, 2043 (2002)] for incompressible flows to compressible flows. We note that the present study is both the first extension of the dynamic concept to compressible flows and also the first test at high Reynolds number flows. The present study also revisits the issue of numerical errors near wall-region on outer-layer coarse LES mesh. The numerical results are compared with wall-resolved LES data (at low Reynolds number case) and available experimental data (at high Reynolds number case). [Preview Abstract] |
Tuesday, November 23, 2010 9:05AM - 9:18AM |
MD.00006: A buoyancy-adjusted extension of the stretched-vortex subgrid-scale model Daniel Chung, Georgios Matheou We present a buoyancy-adjusted extension of the stretched-vortex subgrid-scale (SGS) model suitable for large-eddy simulation (LES) of stratified flows. The model remains free of parameters and is consistent with features of anisotropic mixing frequently observed in stratified flows. The vortex-based construction naturally constrains the mixing in the horizontal provided the vortex alignment is favorable even at high gradient Richardson numbers. We will compare the LES results with direct numerical simulation (DNS) of homogeneous stably stratified flows. [Preview Abstract] |
Tuesday, November 23, 2010 9:18AM - 9:31AM |
MD.00007: Scaling laws in helical rotating turbulence: do they change with Reynolds number? A. Pouquet, J. Baerenzung, P. Mininni, D. Rosenberg In rotating turbulence, the presence of helicity leads to significant differences when compared to flows without global velocity-vorticity correlations, as seen using direct numerical simulations (DNS) with up to $1536^3$ points, down to Rossby numbers $Ro \approx 0.06$. Long-lived laminar structures and turbulent vortices co-exist. The energy undergoes both an inverse and a direct cascade, the latter being self-similar with spectrum $E(k)\sim k^{-e}$ and transfer rate $\epsilon$ and dominated by the helicity cascade (spectrum $H(k)\sim k^{-h}$, transfer $\tilde \epsilon$). This points to the existence of a new small parameter, $\epsilon/[L_0 \tilde \epsilon]$, with $L_0$ a characteristic length. We also find that $e+h=4$, taking into account the inertial wave mediation of nonlinear helicity transfer to small scales, with $e\not=h$ at the intermediate Reynolds numbers at which we compute. Using an isotropic model based on the Eddy Damped Quasi-Normal Markovian closure, and including the contribution of helicity to eddy viscosity and eddy noise, we show that we can recover the DNS results at substantially lower costs and that, at fixed Reynolds number, strong rotation leads to the $e+h=4$ regime whereas $e=h=5/3$ when increasing the Reynolds number at fixed rotation rate. [Preview Abstract] |
Tuesday, November 23, 2010 9:31AM - 9:44AM |
MD.00008: Analysis of Structure Functions for the Turbulent Ekman Layer Direct Simulation Scott Waggy, Sedat Biringen A direct numerical simulation of the low-Reynolds number turbulent Ekman layer was performed to assess the validity of Kolmogorov similarity laws in rotating turbulent flows. The three dimensional mean flow exhibited by the Ekman layer offers complex energy transfers not encountered in simple two-dimensional turbulent flows with one main mean shear direction. Time averaged 2nd order velocity structure functions were calculated to determine the extent of the inertial subrange at low Reynolds numbers. In addition, the constant C$_2$, a universal constant of the structure functions, was compared with non-rotating boundary layers to analyze its applicability to different flows. The degree to which higher order structure functions abide by Kolmogorov's scaling was also analyzed for 3rd and 4th order structures. [Preview Abstract] |
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