Gas Jet Noise Analysis And Suppression Technology In Solid Rocket Of High-burning Rate

Short-duration solid rocket,as a man-portable anti-tank weapon,is used to launch the rocket projectile.High temperature,high speed,high pressure and unsteady complex flow field can be generated by the rocket exhaust plume,and high intensity noise and a long flame are formed.The severe acoustic environment arising from supersonic gas jet of the rocket engine induces serious damage to the surrounding staff and ground facilities,and introduces potential risk for the reliability and safety of the rocket launching.Therefore,it is necessary to devise methods to predict and reduce the noise generated by the gas jet.The relevant theoretical,experimental and numerical studies have been carried out,focusing on the gas jet flow field,aerodynamic noise and the noise reduction scheme on the engineering background of the solid rocket launching.The main research contents and results are as follows:(1)The jet noise generation mechanism and the characteristics are investigated,and the interaction between the flow field and the sound field is described combined with correlation theory such as the gas jet dynamics,the aerodynamic acoustics.Based on the flow equation of the gas jet and the aerodynamic acoustic equation,the prediction model of the gas jet noise and the expression of the sound power are developed.And the influence factors of engine jet noise are discussed.(2)The static experimental platform on the gas jet noise of the rocket engine is designed and built,and the radiation characteristics of the gas jet noise are studied systematically.The diffusion processes of the gas jet in the atmospheric are observed and preliminarily discussed by means of a high speed photographic system.High temperature and high speed gas is constantly mixed with the surrounding atmosphere,the intensity of axial expansion is stronger than that of radial expansion in the jet processes,and the outer contours of the gas jet are very irregular presenting serrated.The distribution laws of the sound pressure at different observation points are collected by using the digital transient recorder.With the increase of the combustion chamber pressure and the nozzle throat diameter,the peak of the sound pressure increases.With the polar angle increasing,the peak sound pressure level decreases.The sound field distribution of the jet noise displays a strong directivity.Due to the impact of the ground on the acoustic wave,the fluctuation of the sound pressure at the test point near the ground is larger.In individual rocket launch process,the gas jet noise has been measured around the launcher tube.The jet noise is analyzed emphatically at the shooter location.The distribution characteristics of the jet noise are revealed in the axial and radial direction.(3)Based on experimental studies,Large Eddy Simulation(LES)is used to simulate the supersonic jet flow.And the distribution characteristics of the velocity,pressure and temperature are obtained.Based on the simulation results of the flow field,the jet noise is predicted by applying the Ffowcs Williams-Hawkings(FW-H)acoustics equation and Fourier transform.The results show that,the complex structures of expansion waves,compression waves and the turbulent boundary layer could occur due to the strong interaction between the gas jet and the ambient air.The main component of the jet noise is in the low frequency region,the sound field distribution of the jet noise has an obvious directivity.The jet noise is the most intense at the polar angle ?=45°,which shows the characteristic of the quadrupole source of the jet noise.By the comparative analysis of calculated and test results,the models and research technique are proved feasibility and accuracy.In addition,the influences of main characteristic parameters like combustion chamber pressure,gas temperature and nozzle size on the jet noise are contrast studied.(4)According to the acoustic characteristic of the jet noise,a simple and effective noise reduction scheme is proposed based on a liquid column driven by the gas jet.And then the noise reduction experiments have been carried out.The diffusion and mixing process of high-temperature high-pressure gas flow in the liquid water column in the air is studied by means of a high speed photographic system.The gas-liquid mixture jet noise has also been measured.The experimental results indicate that,when the liquid water column is put into the tail tube,the jet flow structure is changed and the jet flow parameters(velocity,temperature,etc.)are decreased due to the interaction of the gas jet with the liquid column.In addition,the jet noise is significantly reduced in the presence of the liquid column,compared with the condition without the liquid column.In order to further optimize the noise reduction scheme,the variations of the sound pressure level are discussed as a function of mass of the liquid column.(5)In order to study the process on the interaction of the gas jet with the liquid column,the noise reduction mechanism and other complex problems,the two-phase flow model is established for describing the process of the gas jet driven the liquid column on the basis of experiments.And numerical simualtions have been conducted by LES/OF method.The distribution laws of velocity,pressure and temperature in two-phase flow field are obtained.The calculation results of axial displacement of the jet are in good agreements with experimental results,so the models and research technique are proved feasibility and accuracy.The atomization of liquid column,the unstable motion of droplet and the characteristic of gas-liquid turbulence mixing are analyzed.The effects of mass(volume)and density of the liquid column,combustion chamber pressure on the parameters of two-phase flow field are discussed.The noise reduction scheme of liquid column balance is optimized.