Research Of Aerodynamic Noise Characteristics On Surface Protuberance Of Subsonic Aircraft Fuselage

The surface of the aircraft fuselage inevitably has protuberance and forms complex flow fields,which will affects the noise characteristics of the aircraft fuselage surface.The surface noise of high-strength protuberance affects the normal operation of internal electronic equipment and causes fatigue damage to its own structure,even serious impact on aircraft safety.It can also cause emotional tension,palpitations,and discomfort among onboard personnel;finally,it can increase the risk of aircraft acoustic detection,affecting the stealth(acoustic)performance and strong penetration ability of near ground aircraft,which will lead to serious consequences.Therefore,it is necessary to study the aerodynamic noise characteristics of protuberance on the surface of the aircraft fuselage and analyze their noise effects.It is of great practical significance to conduct aerodynamic noise analysis on the inevitable protuberance structures in the design of the entire aircraft.This thesis uses the Large Eddy Simulation(LES)method to study the aerodynamic noise level of the driver’s rear observation window of a large transport aircraft,revealing the mechanism of aerodynamic noise.In terms of wind tunnel testing,this thesis analyzes the noise levels of different protuberance configurations to obtain the optimal aerodynamic noise configuration.The main content of the thesis includes:(1)Simulation on the aerodynamic noise calculation of protuberance on the surface of subsonic aircraft fuselage is put forward for using a method for mixing RANS and LES(Based on SST k-ω two equation models of LES method).In terms of flow field,using M6 wings to achieve SST k-ω two equation model’s verification,in terms of aerodynamic noise calculation,a typical two-dimensional cylindrical flow is selected to verify the LES method.Finally,the simulation results are compared to the experimental results,proving that the based SST k-ω two equation models of LES method used in this thesis is feasibility for the numerical calculation of aerodynamic noise.(2)Simulation on typical protuberance configurations is carried out with based on SST k-ω model of LES method.After obtaining the pressure pulsation on the surface of the protuberance,a fast fourier transform is performed.By comparing the results of sound pressure level and sound pressure spectrum,the simulation results are in good uniformity with the experimental results,with an deviation basically within the range of about 10%.At the same time,the analysis of velocity,pressure,and vortex structure revealed the main aerodynamic noise source areas and their patterns,as well as the causes of the protuberance on the surface of the fuselage.(3)Research and analysis on the changes in aerodynamic noise levels of different protuberance.Based on the analysis of the noise level of the benchmark protuberance,wind tunnel testing is conducted on a comparison group of protuberance with varying lengths and their noise characteristics are analyzed,the results showed that the protuberance with the largest front part length of 140 mm has the best noise reduction effect,followed by protuberance with a front part length of 120 mm,and protuberance with a front part length of 100 mm had the worst noise reduction effect.Wind tunnel testing is conducted on a comparison group of protuberance with varying angles and their noise characteristics are analyzed,the results showed that the protuberance with no angle change in the front part has the best noise reduction effect,followed by protuberance with an angle change of 30 degrees,and protuberance with an angle change of 60 degrees had the worst noise reduction effect.