Study On The Characteristics And Structure Of Supersonic Jet Noise Reduction

Supersonic jet is widely used in the industrial field.The jet noise produced by supersonic jet will not only seriously affect the performance and life of the surrounding equipment,but also cause great harm to the personnel in the jet noise environment.In this paper,the characteristics of supersonic jet noise and its noise reduction structure are studied to achieve the purpose of reducing jet noise.The main contents of this paper are as follows(1)Using SST K-ω model,the simulation model of supersonic free jet flow field is established.The correctness of the simulation model flow field calculation is verified by theoretical formula calculation and pitot tube test.Based on the calculation of supersonic free jet flow field,les and FW-H models are used to establish the calculation model of supersonic free jet sound field.The sound pressure measured by microphone sensor is compared with the simulated sound pressure to verify the correctness of the sound field model,which lays the foundation for the subsequent sound field calculation.(2)Based on the calculation of supersonic free jet flow field,a broadband noise source model is established,and it is determined that the main sound producing position of jet noise is outside the potential flow core area.Then,using the sound field calculation model of supersonic jet,the sound pressure measuring points are arranged on the jet axis of1500 mm and the circumference of 500 mm.The results show that the sound pressure changes little on the jet axis,and gradually decreases from 0 ° to 90 ° on the circumference.Finally,the sound pressure signal of the circumference measuring point is extracted,and the frequency domain signal of the sound pressure is obtained through the spectrum analysis of the fast Fourier transform.Then,the 1/3 octave spectrum analysis is used to obtain the main frequency band of the jet noise in the range of 2000 Hz to 8000 Hz.(3)According to the analysis results of noise sources and the distribution characteristics of free jet noise,three kinds of noise reduction structures are designed,which are open enclosure,expansion cavity enclosure and anechoic tube,without changing the flow field.By using the sound field simulation model,the sound field simulation calculation of three kinds of noise reduction structures is carried out respectively.The results show that the variation range of sound pressure level affected by the two kinds of acoustic enclosures is within 3d B,and the silencing amount of jet noise by the silencing tube is about 9d B.(4)Based on the structure parameters of the muffler with expansion ratio of 15,the topology optimization model is established.Through topology calculation,the structure parameters of the muffler are optimized.Then,the sound field of the optimized muffler is calculated by using the sound field model of supersonic jet.Compared with the muffler effect before and after optimization,the result of topology optimization is verified to improve the amount of muffler.In order to facilitate processing,the irregular boundary is treated as two kinds of models: the anechoic tube with cone and the stepped anechoic tube,and the sound field is calculated by using the sound field model.The results show that the straight stepped anechoic tube is better,and the noise attenuation of jet noise is about20 d B.