Large Eddy Simulations of Supersonic Impinging Jets

Abstract

Supersonic impinging jet flowfields contain self-sustaining acoustic feedback features that create high levels of discrete frequency tonal noise. These types of flowfields are typically found with short takeoff and landing military aircraft as well as jet blast deflector operations on aircraft carrier decks. The US Navy has a goal to reduce the noise generated by these impinging jet configurations and is investing in computational aeroacoustics to aid in the development of noise reduction concepts. In this paper, implicit Large Eddy Simulation (LES) of impinging jet flow-fields are coupled with a far-field acoustic transformation using the Ffowcs Williams and Hawkings (FW-H) equation method. The LES solves the noise generating regions of the flow in the nearfield, and the FW-H transformation is used to predict the far-field noise. The noise prediction methodology is applied to a Mach 1.5 vertically impinging jet at a stand-off distance of five nozzle throat diameters. Both the LES and FW-H acoustic predictions compare favorably with experimental measurements. Time averaged and instantaneous flowfields are shown. A calculation performed previously at a stand-off distance of four nozzle throat diameters is revisited with adjustments to the methodology including a new grid, time integrator, and longer simulation runtime. The calculation exhibited various feedback loops which were not present before and can be attributed to an explicit time marching scheme. In addition, an instability analysis of two heated jets is performed. Tonal frequencies and instability modes are identified for the sample problems.