Research On Analysis Method For Acoustic Load Field Of Materials And Structures In Aerodynamic Noise Environment

During the high-speed service of the aircraft,the air interacts with the aircraft structure,causing the air pressure on the surface of the aircraft structure to pulsate.As a result,the aerodynamic noise load is generated and gives rise to acoustic fatigue failure of aircraft,threatening the service safety of the aircraft.Therefore,in the research of aircraft design,sound field test and analysis on the aircraft structure is carried out,which can provide the reference for noise reduction design and performance evaluation of service security.In this paper,the aerodynamic noise load field of the material and structure under aerodynamic noise environment is studied in the simulated environment in ground.The acoustic load field analysis method of the material and structure under aerodynamic noise environment is carried out.In the simulated experimental environment,there are some difficulties as follows.The background noise of the airflow is serious,which gives rise to a low signal-to-noise ratio;The aperture of the microphone array is limited in the environment and as a result the identification ability of the sound source is insufficient;The sound path is deflected in the airflow;The near-field test environment is extremely harsh,and it is difficult to obtain the real-time acoustic load signal by means of direct measurement in the near field because of the harsh flow environment.It is of great significance that some existing sound field analysis methods are improved in this paper to increase the accuracy of the methods,which can provide more reliable data to evaluate the service safety and offer the noise reduction design for the aircraft structure.The details of the paper are as follows:(1)A method for suppressing the airflow background noise based on EEMD is proposed.Aiming at the suppression of airflow background noise with high intensity in aerodynamic noise load environtment,a method to suppress the airflow background noise based on EEMD is proposed.First,the pure airflow background noise signal is collected under the condition of airflow without a test piece.Then the test piece is installed in the airflow,and the mixed signal containging the aerodynamic noise of the test piece and the background noise is collected.In the next the mixed signal is decomposed by EEMD to obtain the IMF components,and the correlation coefficient between each IMF component and the pure air background noise signal is calculated.All the IMF components whose correlation coefficients are larger than a threshold are abandoned to realize the background noise suppression.With this method,the identification performance on aerodynamic sound source of test piece under the airflow background noise is improved.The effectiveness of the method is verified by the experiment of airflow background noise suppression in the acoustic wind tunnel when locateing a pair of speakers and aerodynamic noise source at the trailing edge of a wing model.(2)A new method of the aerodynamic noise source localization based on Amiet-IMACS is proposed.Aiming at the localization of aerodynamic noise source for typical aircraft components with high precision,a method to locate the aerodynamic noise source based on Amiet-IMACS is proposed.First,the Amiet method is used to modify the array manifold matrix in the airflow environment.Then on the basis of the cross spectrum matrix fitting method,a new constraint condition is proposed,which can adaptively change the parameters of sparse constraints,to improve the sound source identification and calculation efficiency.The effectivness of the method is verified by the accurate localization result of a pair of correlated sound sources and that of the trailing edge vortex noise source on surface of an airfoil model in an acoustic wind tunnel with a maximum flow speed of 80 m/s.(3)The aerodynamic noise load signal reconstruction method based on Amiet-AP-TR is presented.Aiming at the reconstruction of the real-time acoustic load signal and acoustic load field in aerodynamic noise environment,a method of aerodynamic acoustic load signal reconstruction based on Amiet-AP-TR is proposed.Firstly,the microphone array signal is time reversed,as well as the direction of the airflow.Secondly,the path and delay of the time-reversed acoustic wave in the airflow environment are calculated by Amiet method.And then the real-time sound pressure signal of the acoustic load field can be obtained,and the high time-resolved aerodynamic noise loading field analysis can be realized.The effectiveness of the method is verified by the analysis of the loudspeaker signal reconstruction and that of the aerodynamic noise load field on an airfoil model in an acoustic wind tunnel with a maximum flow speed of 80 m/s.(4)An analysis of aerodynamic noise load field for typical structures in supersonic airflow is conducted.Aiming at the analysis of aerodynamic noise field of typical components in supersonic airflow environments with a flow speed of 4Ma and an amient pressure of 5kPa,a sound field reconstruction system based on microphone array is proposed.This system consists of a 2×6 microphone array and the NI-PXIe data acquisition equipment,which can realize high-speed synchronous acquisition and sound field reconstruction analysis for aerodynamic noise load of typical components in supersonic airflow environment.The EEMD,Amiet-IMACS and Amiet-AP-TR methods are used to realize a refined analysis of the aerodynamic noise loads for plate-shaped and column-shaped test pieces to obtain the frequency,intensity,position and real-time distribution of the aerodynamic noise loads.