Numerical Simulation For Jet Noise

The prediction of turbulence jet noise in a circular spout is processed by the combination of the CFD (Computational Fluid Dynamic) and aeroacoustics. The basic structure of jet flow can be achieved by 3D modeling of the circular jet with the standard k-εturbulent model. The structure can be divided into two parts. One is the core area of the jet, which is less than 6.2 times of the diameter of spout, and in this area the flow velocity has no change generally; The other part is up to 6.2 times of the diameter of spout. This is the main section in which the velocity attenuates regularly along the axes, and the affected area of the jet is expanded. According to the theory of the axisymmetry, the 3D circular jet can be simplified to 2D jet, and then the control equation of the Large Eddy Simulation (LES) can be achieved. What can be obtained by the modeling of the 2D unsteady situation is the instantaneous characteristics of the flow area, including the occurrence, development of the primary vortex and its first and second matching processes. Therefore the main area where the turbulence jet noise being generated is defined as the section from the spout to 10 times of the diameter in the downstream.The characteristics of jet noise are obtained by the combination of the equation of FW-H in aeroacoustics and the result of CFD. With the same diameter of spout and the same flow medium of air, the sound pressure level generated by high pressure is higher than that by the low pressure, but the two levels have the similar spectra, which are shown in the parallel lines of the spectrogram. With the same diameter of spout and the same pressure, the spectra generated by different mediums such as air and vapor are also similar. The change of the pressure has more distinct influence on the noise than the change of medium. The prediction of the high frequency spectrum is less than perfect, due to the limits of calculation ability of the computer and computational method.