Numerical Predictions Of Noise Due To Subsonic Jets From Nozzles With And Without Chevrons

摘要

Numerical simulations of round, compressible, turbulent jets using the Shear Stress Transport (SST k-ω) model have been carried out. The three-dimensional calculations have been done on a tetrahedral mesh with 0.9 million cells. Two jets, one cold and hot, have been simulated. The Mach number for both the cases is 0.75. Overall sound pressure levels (SPL) at far-field observer locations have been calculated using Ffowcs Williams-Hawkings equation. The numerical predictions have been compared with experimental results available in the literature. Axial and radial variation of the mean axial velocity, axial variation of (u'u')~(1/2), (v'v')~(1/2), radial variation of u'v' and overall SPL levels are compared. The potential core length is predicted well, but the predicted centerline velocity decay is faster than the measured value. The URANS calculations are not able to predict the absolute values for the overall SPL, but predict the trends reasonably well. The calculations predict the trends and absolute values of the variations of the spectral amplitude well for the aft receivers, but not for the forward receivers. Effect of chevrons on the noise from the jet is also investigated for cold and hot jets. In each case, two chevron taper angles, namely, 0° and 5° are considered. The latter nozzle produces the most significant modification to the baseline spectra and is less effective at high frequencies in abating the noise. The present calculations predict a reduction in the overall SPL for the chevron nozzle with 0° taper angle and a slight increase for chevron nozzle with 5° taper angle, for both cold and hot jets.