Numerical Prediction of Low Mach Number Jet Noise Ejected From Slit Nozzle

Prediction of the low Mach number jet noise ejected from rectangular nozzle with high aspect ratio is described. Firstly measurement of the jet noise was conducted in semi-anechoic wind tunnel at the low Mach number flow condition. We were found that the sound power of the jet obeyed 6-th power of jet velocity. This means the jet noise is resulted not from quadrupole distribution in the shear flow of jet, but from dipole distribution on the surface of the exit of the nozzle. The model of vortex sound is applied as the sound generation mechanism at numerical simulation. The sound emission from the vortices in the shear flow is modified with the compact Green’s function representing the scattering effect from the surface of the exit of the nozzle in the lower frequency range. It is also modified with the non-compact Green’s function in the higher frequency range. Lastly calculated sound spectra are compared with measured spectra. The comparison will prove effectiveness of this modeling.