Isotropic Turbulence

As an idealized turbulent flow, isotropic turbulence is of great importance for fundamental studies and turbulence model development. We tested various SGS models, including our recently developed nonlinear models, in freely decaying isotropic turbulent cases: a WISC case at a moderate Reynolds number and a JHU case at a high Reynolds number. Testing is performed for the first case through a comparison between direct numerical simulation results and LES results regarding resolved kinetic energy and energy spectrum. In the second case, we examine the resolved kinetic energy, the energy spectrum, as well as other key statistics including the probability density functions of velocities and velocity gradients, the skewness factors, and the flatness factors. Simulations using our nonlinear model are numerically stable, and results are satisfactorily compared with DNS results and consistent with statistical theories of turbulence.