Synthetic freestream turbulence generation at an inflow boundary condition

When simulating internal flows, it is often desirable to examine the effect of freestream turbulence on the fluid dynamics in the problem of interest. One method for generating freestream turbulence of a prescribed intensity and integral length scale is to impose a synthetic turbulence generation inflow boundary condition that perturbs velocity about a defined mean value. The perturbation at every computational point is calculated using an algorithm that preserves spatial and temporal correlation such that the turbulent structures generated at the boundary propagate into the domain and do not immediately diffuse, as would be the case with white noise generation. The perturbations are also calculated such that the energy cascade obeys a modified von Karman spectrum with integral length scales that conform to a prescribed magnitude. In this paper, a synthetic turbulence generator is implemented within the Naval Reserach Laboratory's discontinuous Galerkin finite element method code, JENRE, and its use is demonstrated in two and three-dimensional simulations of the compressible Navier-Stokes equations. Both subsonic and supersonic turbulent inflows are used. It is shown that the turbulence generator is effective at developing and maintaining freestream turbulence of a prescribed intensity and integral length scale.