Imposing Resolved Turbulence in CFD Simulations

In large-eddy simulations, the inflow velocity field should contain resolved turbulence. This paper describes and analyzes two methods for imposing resolved turbulence in the interior of the domain in Computational Fluid Dynamics simulations. The intended application of the methods is to impose resolved turbulence immediately upstream of the region or structure of interest. Comparing to the alternative of imposing the turbulence at the inlet, there is a large potential to reduce the computational cost of the simulation by reducing the total number of cells. The reduction comes from a lower demand for mesh resolution in the upstream part of the domain. The first method uses a modification of the source terms in the discrete Navier-Stokes equations. In the second method, an actuator is used to impose the turbulence. The methods are tested, and the most accurate is shown to be the approach of modifying the source terms. None of the two methods can impose synthetic turbulence with good results, but it is shown that by running the turbulence field through a short precursor simulation, very good results are obtained.