Numerical Simulation of Subsonic and Supersonic Impinging Jets II

This report covers two aspects of impinging jets: heat transfer enhancement and sound source mechanisms. Recent experimental investigations indicate a possible increase of up to 40 % of heat transfer efficiency due to a pulsation of the inlet. However, the underlying physical effects are still unclear. Performing direct numerical simulations, we were able to compute the eigenfrequencies of the impinging jet. Our hypothesis is that pulsating with that frequency leads to a maximal increase of ring vortices and consequently of the heat transfer at the impinging plate. First results of a pulsed impinging jet are shown. In addition, impinging compressible jets may cause deafness and material fatigue due to immensely loud tonal noise. It is generally accepted that a feedback mechanism is responsible for impinging tones. However, it is being discussed which mechanism creates those strong pressure waves. Using direct numerical simulations we were able to identify the source mechanism for under-expanded impinging jets with a nozzle pressure ratio of 2.15 and a plate distance of 5 diameters. We found two different types of interactions between vortices and shocks to be responsible for the generation of the impinging tones.