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 BQ: Turbulence Modeling: LES II |
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Chair: Blair Perot, University of Massachussets Room: Hilton Chicago Stevens 2 |
Sunday, November 20, 2005 10:56AM - 11:09AM |
BQ.00001: One-equation LES modeling of rotating turbulence Hao Lu, Christopher Rutland, Leslie Smith Experiments and DNS of rotating turbulence forced at small scales exhibit transfer of energy to large scales in the form of cyclonic vortical columns. We examine the ability of various LES sub-grid stress (SGS) models to reproduce this phenomenon. In particular, one-equation SGS models allow the input of sub-grid kinetic energy that can be transferred to resolved scales via a production term. We have studied SGS models from two main perspectives: (i) consistency with the constraints of material frame indifference (MFI), and (ii) the capability to capture the cyclonic vortices. Two MFI one-equation SGS models that require no assumptions regarding isotropy are tested and compared with the Smagorinsky model, the dynamic Smagorinsky model, the scale-similarity model, the gradient model and the sub-grid kinetic energy viscosity model. In a-priori tests of isotropic decay and forced rotation, the new models perform better when comparisons are made of the regression coefficients. The models also perform better in a-posteriori tests of decaying isotropic and rotating turbulence. Preliminary simulations of rotating turbulence forced at small scales show that the models are able to capture the important flow characteristics. [Preview Abstract] |
Sunday, November 20, 2005 11:09AM - 11:22AM |
BQ.00002: Characteristics of 1d spectra in finite-volume large-eddy simulations with `one-dimensional turbulence' subgrid closure Randy McDermott In this talk we illuminate the reasons behind curious characteristics of the one-dimensional (1d) spectra for coupled `one-dimensional turbulence' (ODT) and large-eddy simulations (LES) and propose a means of correcting the ``spectral dip'' in the ODT transverse 1d spectrum. When the ODT model of Kerstein et al. [JFM 2000] is used as a subgrid closure for LES the characteristics of the three-dimensional (3d) LES spectrum significantly impact the shape of the ODT 1d spectra in the wavenumber range close to the LES grid Nyquist limit. For isotropic fields the 1d spectra (e.g., E22(k1)) will contain contributions from the 3d spectrum, E(k), from wavenumbers k = k1 to k = infinity. If the LES field is filtered using a spectral cutoff, Gaussian, or box filter then the attenuation of the 3d spectrum at high wavenumbers produces a ``spectral dip'' in the ODT 1d spectrum near the LES Nyquist limit. This problem can be alleviated by using a different LES filter kernel. Fortuitously, the resulting shape (i.e., ``implied filter'') of the 3d spectra produced by the Harlow and Welch numerical method [Phys. Fluids 1965] (i.e., second-order staggered energy conserving scheme without explicit filtering) eliminates the dip problem. [Preview Abstract] |
Sunday, November 20, 2005 11:22AM - 11:35AM |
BQ.00003: Variational multiscale formulation of LES on unstructured meshes Carlos Colosqui, Assad Oberai The variational multiscale (VMS) formulation of large eddy simulation (LES) is a new approach to LES which relies on variational projections rather than filters to accomplish scale separation. In addition, in this approach the resolved scales are subdivided into coarse and fine scale components, and different models are utilized for their evolution. The implementation of this formulation using spectral methods is relatively straightforward, and over the last few years several encouraging results have been reported. In this talk, motivated by the eventual application of the VMS formulation of LES to flows in complex geometries, we present a finite element implementation for the incompressible Navier Stokes equations. We describe important features of our formulation and report results for the 3-D lid-driven cavity flow at Re=10,000 on fully unstructured meshes. [Preview Abstract] |
Sunday, November 20, 2005 11:35AM - 11:48AM |
BQ.00004: far-field acoustic properties of LES John Wanderer, Assad Oberai Several large eddy simulation (LES) models were evaluated with respect to their ability to predict far-field noise generated by sustained homogeneous isotropic turbulence. The far-field acoustic pressure was determined using an analytical solution of Lighthill's acoustic analogy resulting in an expression for the wavenumber-frequency spectra of the acoustic intensity in terms of a forth-order, two-point statistic of the incompressible velocity field. The ability of various LES models to accurately replicate this statistic was compared against results from direct numerical simulations. In the comparison, the Smagorinsky (constant coefficient and dynamic) and several variants of the variational multiscale formulation (constant coefficient and dynamic) were considered. [Preview Abstract] |
Sunday, November 20, 2005 11:48AM - 12:01PM |
BQ.00005: Using a RANS model to Perform LES of Isotropic Decaying Turbulence Blair Perot, Jayson Gadebusch The performance of a slightly modified k/$\varepsilon $ model is demonstrated on the problem of isotropic decaying turbulence on mesh sizes ranging from 1$^{3}$ to 64$^{3}$. The model automatically performs RANS, URANS, VLES or LES depending on the mesh resolution. The transition in model behavior is natural and very smooth. No \textit{ad hoc} functions or blending parameters are used to obtain the change in model type from RANS to LES. Perhaps most importantly, the mesh size does not appear in this model even in the LES limit. Moreover, it is demonstrated that the model asymptotically obtains the same balance between resolved and unresolved kinetic energy for a particular mesh size irrespective of the initial conditions. The implications for Unified RANS/LES modeling are discussed. *Supported by AFOSR Grant FA9550-04-1-0023 managed by Lt Col Rhett Jefferies. [Preview Abstract] |
Sunday, November 20, 2005 12:01PM - 12:14PM |
BQ.00006: Intermittency of Acceleration in Second-Order Sto\-chastic Lagrangian Models Andrea G. Lamorgese, P.K. Yeung, Stephen B. Pope Accounting for intermittency of dissipation has been shown useful in the stochastic Lagrangian modelling of fluid particle accelerations in high Reynolds number, stationary isotropic turbulence (A.M.~Reynolds, \textit{Phys.~Rev.~Lett.}~{\bf 91}(8), 084503 (2003)). We have identified a class of Markovian stochastic models (conditional on a log-normal representation for the pseudo-dissipation) that are exactly consistent with Gaussian velocity statistics and conditionally-Gaussian acceleration statistics. One subclass of models is defined by Kolmogorov (1962) scaling of the conditional acceleration variance, with acceleration and the logarithm of pseudo-dissipation coupled via a cross-diffusion coefficient that is linear in acceleration. The Reynolds (2003) model belongs to this class. The stochastic model formulation allows for deviations from Kolmogorov (1962), as observed in DNS data on the conditional acceleration variance. Different specifications for a conditional velocity (or acceleration) timescale are investigated for the matching of conditional two-time acceleration and velocity auto- and cross-correlations from DNS up to $2048^3$ modes. Such data support a representation of the logarithm of pseudo-dissipation as an Ornstein-Uhlenbeck process. [Preview Abstract] |
Sunday, November 20, 2005 12:14PM - 12:27PM |
BQ.00007: Investigation of SGS modeling approaches for scalar transport and mixing in LES O.S. Sun, L.K. Su, T. Burton In large-eddy simulation (LES) of non-premixed combustion, accurate determination of subgrid scale (SGS) quantities, including subgrid scalar flux, variance and dissipation rate, is crucial for predicting both large and small scale mixing phenomena. Some previous studies have examined appropriate methods for predicting and analyzing SGS model behavior.\ \footnote{Jim\'{e}nez, C. \emph{et al.} \emph{Phys.Fluids} \textbf{13}, 2433 (2001); Meneveau, C. and Katz, J. \emph{Annu.\ Rev.\ Fluid Mech.} \textbf{32}, 1 (2000); Liu, S. \emph{et al.} \emph{J.\ Fluid Mech.} \textbf{275}, 83 (1994)} However, there are currently no universal metrics for assessing the performance of SGS models and, in particular, SGS scalar mixing models. Here, we perform LES of passive scalar mixing in a spatially developing, free, round turbulent jet. The LES code is based on a spherical coordinate direct numerical simulation (DNS) code. Different SGS models are used to close the subgrid scalar flux term in the scalar transport equation, including eddy diffusivity, scale similarity, and mixed models. Models for the subgrid scalar variance and scalar dissipation rate, necessary for combustion simulations, are studied as well. The primary objectives are to examine the physical implications of SGS mixing models and determine major factors influencing model performance. Results from the LES are compared with DNS as well as experimental measurements of velocity and scalar fields. [Preview Abstract] |
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