Acoustic shielding and interaction effects for strongly heated supersonic twin jets

The effects of jet interactions and acoustic shielding on the noise of strongly heated supersonic twin jets are studied using large-eddy simulations. For that purpose, one single jet and three twin jets separated by distances of 2, 2.4, and 2.8 jet diameters are considered at a Mach number of 3.1 and a stagnation temperature of 2000 K. The twin jets interact and merge near the end of their potential cores at a position that is shifted downstream when the nozzle spacing increases. For larger nozzle spacing, the turbulence rates in the plane containing the jets are higher whereas those in the jet midplane are lower. In the near pressure field, the overall acoustic power radiated by the twin jets is lower than that for two non-interacting single jets, which indicates that some of the sound sources are weakened by jet interactions. A maximum noise reduction of 2 dB is reached in the jet plane, where the acoustic waves produced by one jet are shielded by the other one. Despite the overall noise reduction, some noise components are stronger for the twin jets, suggesting that they generate additional interaction noise. This is the case for the broadband shock-associated noise component and for the noise radiated at low polar angles in the jet midplane. The intensity of interaction noise increases with the nozzle spacing and varies with the turbulence rates in the inner shear layers at the axial position where the twin jets interact.