Large Eddy Simulation of High Speed Nozzle Flows - Assessment & Validation of Synthetic Turbulence Inlet Conditions

Abstract

An improved method for synthetic inlet condition generation for Large Eddy Simulation (LES) predictions of nozzle flows is described. This is based on a rescaling/recycling method (R 2 M). Preliminary results reveal the benefits of this method such that self-consistent, correlated turbulent structures were sustained throughout the high acceleration region associated with nozzle convergence, with the turbulence anisotropy developing in the expected manner. 1 st and 2 nd moment statistics at nozzle inlet from the R 2 M approach were in good agreement with the experimental target profiles. LES predictions using a standard Smagorinsky closure for the sub-grid-scale (SGS) model show that the level of turbulence energy obtained at nozzle exit is less than measured, but this is sensitive to the constant and filter width assumed in the SGS model. The LES results for velocity profile shape at nozzle exit are better than low Re Reynolds Averaged Navier Stokes (RANS) predictions. A recently proposed SGS model that defines the SGS length scale based on local turbulence quantities and hence produces a mesh independent formulation for the SGS viscosity is also applied to the nozzle flow test case and results show significant improvement in the turbulence energy development through the nozzle.