Hybrid LES/RANS methods for the simulation of turbulent flows

Inlet conditions for large eddy simulation: A review

http://www.urbanphysics.net/2011_AE_PG_BB_TS_GvH_Montreal__Preprint.pdf

CFD simulation of near-field pollutant dispersion on a high-resolution grid : a case study by LES and RANS for a building group in downtown Montreal

The paper presents the detailed formulation and validation results of simple and robust procedures for the generation of synthetic turbulence aimed at providing artificial turbulent content at the RANS-to-LES interface within a zonal Wall Modelled LES of attached and mildly separated wall-bounded flows. There are two versions of the procedure. The aerodynamic version amounts to a minor modification of a synthetic turbulence generator developed by the authors previously, but the acoustically adapted version is new and includes an internal damping layer, where the pressure field is computed by “weighting” of the instantaneous pressure fields from LES and RANS. This is motivated by the need to avoid creating spurious noise as part of the turbulence generation. In terms of pure aerodynamics, the validation includes canonical shear flows (developed channel flow, zero pressure gradient boundary layer, and plane mixing layer), as well as a more complex flow over the wall-mounted hump with non-fixed separation and reattachment, with emphasis on a rapid conversion from modeled to resolved Reynolds stresses. The aeroacoustic applications include the flow past a trailing edge and over a two-element airfoil configuration. In all cases the methodology ensures a very acceptable accuracy for the mean flow, turbulent statistics and, also, the near- and far-field noise.

Synthetic Turbulence Generators for RANS-LES Interfaces in Zonal Simulations of Aerodynamic and Aeroacoustic Problems

Experimental and numerical investigation of a three-dimensional vertical-axis wind turbine with variable-pitch

The Vortex Method (VM) based boundary condition of Sergent (2002) was implemented in the general purpose CFD solver Fluent. It is shown that the VM offers a relatively inexpensive and accurate way to generate random fluctuations representing a turbulent flow field at the inlet. Since the generated velocity field is temporally and spatially correlated, it is a much more realistic representation of turbulence than the one obtained with a simple velocity distribution, using a random generator. Validations are reported for fully developed turbulent channel flow, pipe flow and separated hill flow.

Fabrice Mathey

Papers

Assessment of the vortex method for Large Eddy Simulation inlet conditions