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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenWed, 31 Jan 2024 19:28:33 +0000Large-eddy simulation using a vortex-based subgrid stress model
https://resolver.caltech.edu/CaltechETD:etd-08102005-134328
Authors: {'items': [{'email': 'ashish.misra.07@gmail.com', 'id': 'Misra-A', 'name': {'family': 'Misra', 'given': 'Ashish'}, 'show_email': 'NO'}]}
Year: 1998
DOI: 10.7907/0J91-NE77
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
A class of subgrid-stress (SGS) models for large-eddy simulation (LES) are presented based on the idea of structure-based subgrid-stress closure. The subgrid structure of the turbulence is assumed to consist of stretched vortices whose orientations are determined by the resolved velocity field. An equation which relates the subgrid stress to the structure orientation and the subgrid kinetic energy, together with an assumed Kolmogorov energy spectrum for the subgrid vortices, gives a closed coupling of the SGS model dynamics to the filtered Navier-Stokes equations for the resolved flow quantities. The subgrid energy is calculated directly by use of a local balance between the total dissipation and the sum of the resolved-scale dissipation and production by the resolved scales. Simple one- and two-vortex models are proposed and tested in which the subgrid vortex orientations are either fixed by the local resolved velocity gradients, or rotate in response to the evolution of the gradient field. These models are not of the eddy viscosity type. The choice of the energy spectrum introduces the Kolmogorov prefactor as a parameter. In the simplest case we make an a priori choice of the Kolmogorov prefactor which we refer to as the fixed [...] scheme. Alternatively, one can compute the Kolmogorov prefactor dynamically by enforcing continuity of the resolved energy spectrum with the subgrid spectrum. This introduces an additional equation for the Kolmogorov prefactor which is solved in conjunction with the equation relating the dissipation. This is referred to as the coupled [...] scheme. LES calculations with the present models are described for [...] decaying turbulence and also for forced [...] box turbulence at Taylor Reynolds numbers, [...], in the range [...] (fully resolved) to [...], = [...]. The models give good agreement with experiment for decaying turbulence and produce negligible SGS dissipation for forced turbulence in the limit of fully resolved flow.
Using the coupled [...] scheme, we present LES results for a three-dimensional channel flow. The coupled [...] scheme is implemented in planes of constant height and the Kolmogorov prefactor is calculated as a function of the wall-normal direction by computing a two-dimensional energy spectrum. Results are presented for the alignment models in an open channel of dimensions [...] at a Reynolds number (based on the friction velocity and the channel half width), [...] = 180 and a grid resolution of 32 x 32 x 65, where the last index refers to the wall-normal direction. Results compare favorably with direct numerical simulation (DNS).
https://thesis.library.caltech.edu/id/eprint/3082