Broadband Noise Characteristics Analysis Of Macro-array Structure At Airfoil Leading Edge In High/Low Speed Flow Field

Aerodynamic noise of turbomachinery rotors is one of the main noise sources in people’s daily life and work.Although there are significant differences in the overall dimensions and working conditions of turbomachinery,the main noise source units are airfoil,especially the leading and trailing edges.Therefore,the generation and reduction mechanism of aerodynamic noise around airfoil has become a common concern.Inspired by the convex hull structure of the humpback whale’s head,an array spoiler structure was installed on the leading edge of the NACA0012 airfoil to study its impact mechanism on blade aerodynamic broadband noise under different inflow speeds.Firstly,the open source aeroacoustic noise prediction coupling algorithm used is verified by using the experimental data of the general models,including the tandem cylinder,rod-airfoil,and NACA0012 airfoil.Subsequently,combined with the experimental data at low-speed(20～30m/s),the airfoil noise reduction mechanism of the spoiler airfoil was analyzed by simulation.Finally,at high-speed(0.7Ma),the aerodynamic noise characteristics of the airfoil of the array structure were studied.The main contents and results are as follows.(1)(Algorithm verification)Based on the open source Open FOAM(Open Source Field Operation and Manipulation)fluid dynamics computing platform,a numerical simulation model for LES(Large Eddy Simulation)/FW-H(Ffowcs Williams Hawkings analysis)aerodynamic noise mixing prediction of permeable surfaces was constructed.The accuracy of the hybrid numerical prediction model method was verified using existing experimental data of the tandem cylinders,rod-airfoil and single airfoil.The comparison results show that the model can effectively predict the noise spectrum characteristics.(2)The influence of geometric parameters of the array spoiler structure on the internal flow characteristics of wall boundary layers was studied on a flat plate structure.Taking the side length,height,and number of rows of square columns in the array spoiler structure as the main factors,DOE(Design of Experience)parameter experimental analysis was conducted to determine the primary and secondary order of the array spoiler structure on the internal flow.The result was height>number of rows>side length.The design form and geometric parameters of the airfoil leading edge array spoiler configuration are guided by the results.(3)An array spoiler structure is symmetrically arranged on the upper and lower surfaces of the leading edge position of the NACA0012 airfoil.Based on the LES/FWH acoustic noise prediction model,the experimental results of two airfoil with low speed(20～30m/s)and zero degree angle of attack were compared and verified.The experimental and numerical simulation results showed that the array spoiler structure can reduce the broadband noise of the flow field.Secondly,the noise reduction mechanism of the array spoiler structure was further clarified through the flow evolution characteristics of the boundary layer of the airfoil.The results show that the array turbulence structure significantly weakens the coherence of the spanwise pressure on the blade surface,effectively promoting the occurrence of the phenomenon of transition.Moreover,with the increase of incoming flow velocity,the airfoil with the array structure showed good noise reduction effect.With the increase of the height of the square column in the array spoiler,the noise reduction effect gradually becomes apparent.However,the change of the number of square columns in the array spoiler structure has little effect on the overall noise reduction.(4)The aerodynamic noise characteristics of the airfoil under a high speed compressible(0.7Ma)were investigated using the noise method.It is found that the airfoil with the array structure has significantly higher far field broadband noise peaks than smooth airfoil,and the airfoil with the array structure does not significantly reduce the coherence of spanwise monitoring points in the wall boundary layer in high speed flow fields.However,according to the spectral distribution of noise at different envelope far field detection points on the airfoil wall and the flow field region near the airfoil,it shows that the noise of the body sound source in the wake region of the airfoil under high-speed conditions is significantly higher than that of the wall surface sound source at corresponding frequencies.