Journal
JOURNAL OF FLUID MECHANICS
Volume 747, Issue -, Pages 518-544Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2014.168
Keywords
low-dimensional models; turbulence simulation; wakes
Categories
Funding
- Trafikverket (Swedish Transport Administration)
- PSA Peugeot Citroen
- ANRT
- Chalmers Sustainable Transport Initiative
- Institute PPRIME
- French Agence Nationale de la Recherche (ANR)
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We investigate a hierarchy of eddy- viscosity terms in proper orthogonal decomposition (POD) Galerkin models to account for a large fraction of unresolved fluctuation energy. These Galerkin methods are applied to large eddy simulation (LES) data for a flow around a vehicle-like bluff body called an Ahmed body. This flow has three challenges for any reduced-order model: a high Reynolds number, coherent structures with broadband frequency dynamics, and meta-stable asymmetric base flow states. The Galerkin models are found to be most accurate with modal eddy viscosities as proposed by Rempfer & Fasel (J. Fluid Mech., vol. 260, 1994a, pp. 351-375; J. Fluid Mech. vol. 275, 1994b, pp. 257-283). Robustness of the model solution with respect to initial conditions, eddy-viscosity values and model order is achieved only for state-dependent eddy viscosities as proposed by Noack, Morzy n nski & Tadmor (Reduced-Order Modelling for Flow Control, CISM Courses and Lectures, vol. 528, 2011). Only the POD system with state-dependent modal eddy viscosities can address all challenges of the flow characteristics. All parameters are analytically derived from the Navier- Stokes-based balance equations with the available data. We arrive at simple general guidelines for robust and accurate POD models which can be expected to hold for a large class of turbulent flows.
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