High-Fidelity Numerical Simulation of a Chevron Nozzle Jet Flow

Abstract

We report results from the simulation of a moderate Reynolds number cold jet flow exhausting from a chevron nozzle with six symmetric chevrons that have an approximately 18-degree penetration angle. The flow inside the nozzle geometry and the free jet flow outside are computed simultaneously by a high-order accurate, multi-block, large eddy simulation code with overset grid capability. The simulation is performed on 400 million grid points using 2048 processor cores in parallel. The main emphasis of the simulation is to compute the jet flow in maximum detail possible and accurately capture the physical processes that lead to noise generation. It is especially critical to capture the enhanced shear layer mixing due to chevrons that takes place within the first few diameters downstream of the nozzle exit. Our calculations resolve the jet flow field at an unprecedented level of detail. Despite some issues such as an order of magnitude lower simulation Reynolds number (relative to experimental value) and unknown turbulence intensity levels within the experimental nozzle, it is shown that both the near-field jet turbulence and far-field noise predictions are in good agreement with the experimental measurements. Because of the enormous number of grid points required to resolve the near-nozzle region, the computational domain size is constrained to ten nozzle exit diameters downstream of nozzle exit by the limited computational resources. As a result, not all of the low frequency generating noise sources are resolved in the calculation, resulting in some errors in the low frequency range of the predicted noise spectrum. Nevertheless, it is shown that the high frequency noise generation in the near-nozzle region is predicted quite well.