Simulations and experiments of dual high-speed impinging jets

Aeroacoustic characteristics of small diameter high-speed impinging jets are investigated experimentally and numerically. A single round jet perpendicularly striking a flat surface generates loud, tonal noise due to the resonance between instabilities in the jet shear layer and acoustic feedback from the impingement plate. The addition of a second impinging jet placed laterally near to the first disrupts this tone generating mechanism. These phenomena are investigated experimentally using Schlieren imaging and near-field microphone measurements. We also apply high-fidelity Large Eddy Simulation (LES) using unstructured meshes to resolve the entire three dimensional flow field and compare to experimental measurements. We consider under expanded cold jets of design Mach numbers 1 and 1.5 operating in isolation, as well as a flow field where the two jets are laterally placed at 4.5 jet diameters. We investigate the acoustic properties of the simulated flow fields by extracting frequency information from pressure measurements in the shear layer. We identify shear layer features that are most significant in generation of near-field noise.