Supersonic Jet Study On Wave Packet Evolution And Acoustic Radiation In Supersonic Jet

Jet noise is a hot topic in the field of aeroacoustics in this century.The research on jet noise has important guiding significance for improving environmental quality and improving the performance of aviation equipment.Computational aeroacoustics is in the ascendant.Computational aeroacoustics is not only a computational method,but also a physical problem.It is necessary to understand the physical mechanism of noise generation and propagation.In this paper,a new aeroacoustic hybrid algorithm for supersonic(MA = 2.1)jet is developed and improved.Compared with the traditional aeroacoustic mixing algorithm,its advantage is that it can not only save calculation time,but also explain the mechanism of jet noise more clearly.The flow near-field is solved by nonlinear perturbation equation(NLDE)/ parabolic stability equation(NPSE).The acoustic far-field is calculated by Wu integral theory.The evolution of two-dimensional axisymmetric mode wave packet and three-dimensional helical mode wave packet in the flow field and acoustic radiation are analyzed.The calculated sound radiation direction angle and SPL value are consistent with the experimental results,and the predicted sound source location is also consistent with the experimental observation.It shows that the hybrid algorithm is accurate and effective.The main conclusions are as follows:(1)By simulating the axisymmetric mode wave packet in natural jet and excited jet,it is found that the contribution to acoustic far-field mainly comes from the linear growth part of wave packet.The low-frequency wave generated by nonlinear effect has strong growth ability,which makes the acoustic radiation energy gradually transfer to the low-frequency component and increases the acoustic radiation range.The acoustic radiation intensity of the excited jet is greater than that of the natural jet.(2)In the near-field evolution and far-field acoustic radiation,the spiral mode wave packet is obviously affected by the nonlinear effect,and the nonlinear effect increases with the increase of frequency.In particular,the sound field of St = 0.4,which has the strongest radiation ability,is diffracted by nonlinear effect.When the frequency is higher,the first spiral mode does not occupy the dominant position of acoustic radiation,and the second spiral mode also contributes to the sound energy.(3)The acoustic radiation direction angle corresponds to the direction of the maximum sound pressure value,and the direction angle is related to the frequency and disturbance mode.At the same frequency,the direction angle and sound pressure intensity of axisymmetric mode and spiral mode are slightly different.The acoustic radiation concentration of axisymmetric mode is stronger than that of spiral mode,and the acoustic radiation concentration of high frequency disturbance is stronger than that of low frequency disturbance.