Flow Field And Sound Field Characteristics Of Laminar Airfoil Under The Interaction Of Sound Vortex

Multi-layered layered flow wing type industrial area under construction,small unmanned aerial vehicle,wind turbine,the operating Reynolds number range is 10~4<Re<10~6,When these devices operate at this Reynolds number,they produce significant tonal aerodynamic noise.As people’s requirements for noise pollution become higher and higher,noise is required to be further reduced,so it becomes meaningful to study the mechanism of producing tonal noise for laminar airfoil,providing a theoretical basis for noise reduction.The related literature shows that there is a nonlinear interaction between the sound field and the flow field,and the LBM-LES method based on the combination of the two methods of Lattice Boltzmann Method(LBM)and Large Eddy Simulation(LES)is used.,directly calculate the flow field and sound field of NACA0012 airfoil.The sub-lattice model of the large eddy simulation method is a dynamic Smagorinsky model,and the wall flow is directly solved.The angle of attack is 2~°,the laminar flow Mach number is 0.1,and the Reynolds number is 2e~5.The analysis of the calculation results of the flow field shows that there is flow separation on the suction surface of the airfoil,laminar separation bubbles are generated,transitions occur in the separated boundary layer,and vortices are generated,and the vortices exist on the trailing edge of the airfoil fall off periodically.In the transient pressure field,there is a disturbance on the wall of the suction surface,and it is obtained from the analysis of the variation of the pressure fluctuations on the wall.The reason for the change is related to the separation of the wall flow.The strength of the pressure pulsation RMS can also explain the magnitude of the noise,so that the sound source is located at the separation zone of the trailing edge of the airfoil suction surface.By setting monitoring points in the boundary layer of the pressure and suction surfaces,in the wake and the far field,based on the direct calculation method of the sound field of the large eddy simulation,the sound pressure level spectrum of the monitoring points can be obtained.There is discrete pure tone noise in the boundary layer and in the far field,but there is no obvious discrete pure tone noise in the wake region.The main frequency of discrete noise is 750Hz and the subharmonic frequency is 1500Hz.The main frequency and the vortex shedding frequency are similar,indicating that the generation of pure-tone noise is related to the vortex shedding.Comparison and analysis of the pressure power spectral characteristics of the monitoring points in various places,it is found that the spectrum of the strong spectrum and the far-field sound field in the boundary layer of the airfoil suction surface and the pressure surface are similar.But the amplitudes are not the same;the pressure spectrum of the flow field and the far-field noise are not similar in the wake region far from the trailing edge of the airfoil,and there is no discrete dominant frequency with a large amplitude;this indicates that The interaction between the sound field and the flow field is the channel of the vortex interaction.This channel is not related to the wake of the airfoil and ends near the trailing edge of the airfoil.