FAR FIELD NOISE PREDICTION OF SUBSONIC HOT AND COLD JETS USING LARGE-EDDY SIMULATION

Large eddy simulations are performed for hot and cold single stream jets with an acoustic Mach number of(M-a = Vj / a(infinity) = 0.875). The temperature ratio (T-j/T-infinity) for the hot jet is 2.7 and for the cold jet it is 1.0. Grids with 34 million points are used. The simulation results for the flow field are in encouraging agreement with the mean velocity and Reynolds stress measurements. The Ffowcs Williams-Hawkings (FW-H) equation is used to predict the far-field noise. In this study four cylindrical FW-H surfaces around the jet at various radial distances from the centreline are used. The FW-H surfaces are closed at the downstream end with multiple endplates. These endplates are at x = 25.0D - 30.0D with Delta = 0.5D apart. It is shown that surfaces close to jet get affected with pseudo sound. To avoid pseudo sound, surfaces must be placed in the irrotational region. To account for all the acoustic signals end plates are necessary. However, a simple averaging process to cancel pseudo sound at the end plates is not sufficient.