Synthesis and Advection of Isotropic Turbulence to a Target Intensity and Spectrum

Abstract

An isotropic turbulent flow field was synthesized and advected to a targeted turbulence intensity and wave number spectrum using a large eddy simulation (LES). The turbulence was synthesized at the inflow boundary of the computational domain using the Random Flow Generation (RFG) technique. In this particular implementation of the RFG method, the turbulent velocity fluctuations are synthesized from samples of a Gaussian velocity distribution that is deconstructed into its Fourier harmonics. The synthesized turbulence was then advected downstream to a spatial location where a target turbulence intensity and wave number spectrum were specified. Controllable parameters at the inflow boundary were inflow turbulence intensity and length scale. These two parameters, along with the size and spatial resolution of the computational domain, and the advection time step, were varied until the target turbulence intensities and spectrum were achieved. In the LES technique, the filtered, incompressible Navier-Stokes equations were discretized using a second order, bounded central difference scheme. Time advancement was implicit and second order accurate using a fractional step method. The sub-grid scale turbulence was accounted for with a dynamic Smagorinsky model. The final turbulence intensity and wave number spectrum are reasonably close to the targeted values.