The generation of 'synthetic turbulence' for inflow conditions in Large Eddy Simulation is investigated. The method is based on a 2D vortex method for the lateral components of the fluctuating velocity and a 1D Langevin equation for the streamwise velocity component, mimicking a Restress transport model. Channel flow at Re τ = 395 and pipe flow at Re τ = 360 are used to test the 'synthetic turbulence' alone in the 2D inlet plane, then LES computations are run with these inlet conditions. Finally, the method is applied to a backward facing step with and without heat transfer.
The flow around a trailing edge is computed with a new hybrid method designed to more clearly separate the effects of total and sub-grid turbulent stressmodelling on the time-averaged and instantaneous velocity fields, and in turn, mean momentum and kinetic energy balances. These two velocity fields independently define Reynolds averaged and sub-grid-scale viscosities, and distinct stresses, at the same location. In particular, resolved eddies can emerge, or sweep in and out of the Reynolds averaged near wall layer, without being dampened by higher levels of the viscosity in this RANS dominated layer. The two-field hybrid model, first tested on channel flows, gives accurate predictions of mean velocities and stresses for different Reynolds numbers and coarse meshes. For the trailing edge flow the results of the hybrid model are close to the reference fine LES for mean velocity and turbulent content, whereas the DES-SST on the same coarse mesh gives too early separation.
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