Numerical Prediction of Near-field Noise and Return Acoustics from Sonic Jets in Different Operating Conditions

The emitted noise (sound) by turbulent supersonic jet flow coming out from convergent or convergent-divergent nozzles has destructive effects on the environment and humans. To prevent these effects, the noise generation mechanisms should be well studied in the near field and behind the nozzle. In this study, a choked nozzle and its emitted noise are studied in two dimensions using the URANS approach and the k-ε Realizble turbulence model. The noise from the turbulent jet in the near field and behind the nozzle is also obtained by solving the Williams-Hawking equation. The effect of nozzle pressure and temperature on the radiated noise has been investigated. The temperature changes affect the shear layer and the length of the jet potential core. The recorded noise close to the nozzle lip and behind the nozzle indicate that the presence of shock cells in the jet plume affects the acoustic waves propagate upstream. It causes broadband shock cell-associated noise. This noise is about 100 db for a cold jet with a temperature of 300 K and about 105 db for a hot jet with a temperature of 600 K. By increasing the nozzle pressure twice the initial value the noise reaches about 124 db.