Study On The Lattice Boltzmann Method For Computational Aeroacoustics

Aerodynamic noise is one of the main sources of aircraft’s noise,which is related to the comfort and safety and the airworthiness of the aircraft.With the aerodynamic noise of airplanes gradually gaining people’s attention,computational aeroacoustics(CAA)has become focuses of study.Due to the characteristics of acoustic problems,computational aeroacoustics faces a series of problems and challenges,which has strict requirements not only on the computational accuracy,dispersion and dissipation of numerical schemes,but also on the implementation of boundary conditions and the grid resolution.Given the Lattice Boltzmann Method(LBM)presents some advantages,including the low numerical dispersion and dissipation and it’s easy to implement complex boundary conditions and parallel computation and it has corresponding methods for non-uniform meshes,this paper proposes LBM for the direct acoustic simulation.Based on LBM,this paper conducts direct aeroacoustic simulation on the classic acoustic propagation problems,multipole source propagation problems,and the noise generation and propagation problems of complex configuration in non-uniform meshes,which expands the LBM in the study of computational aeroacoustics.The following studys are carried out in this paper:1.The study on acoustic waves propagation based on the single relaxation time model(LBGK)and multiple relaxation time model(MRT)combined with the implementation of traditional acoustic source method and acoustic multipole source(AMS)method is conducted.The results show that the LBGK and the MRT model with quartic parameters possess nearly the same results and agree well with the analytical solutions in simulation of the 2D/3D Gaussian waves and the acoustic periodic point sources.While the results of original MRT model are in poor agreement with the analytical solution due to the existence of bulk viscosity.In the simulation of acoustic multipole source under inviscid limit combined with AMS method,the quartic MRT has better stability than other models,and the results agree well with the analytical solution,also the contour and directivity of sound field clearly show the acoustic characteristics of the acoustic multipole source.2.The study of simplified Lattice Boltzmann Method(SLBM)for computational aeroacoustic is the first time to be carried out,and an implementation method of SLBM combined with AMS method is proposed.Results show that the SLBM method can simulate the canonical test cases including the plane waves,two-dimensional Gaussian waves,and the acoustic periodic point sources,the computational results agree well with the analytical solutions.Also,the acoustic monopole,dipole and quadrupole point sources under inviscid limit can be simulated without spurious fluctuation by the implementation of SLBM combined with AMS,and the results agree well with the analytical solution,which proves the SLBM scheme possesses good stability.Conducting accuracy analysis of the result of Gaussian waves simulated by SLBM,the relative error of SLBM can reach the second-order numerical accuracy.3.For the traditional LBM can’t simulate the aeroacoustic problem of complex objects,the Generalized Form of the Interpolation-Supplemented Lattice Boltzmann Method(GILBM)was applied to perform direct acoustic simulation on complex configurations.By doing the numerical simulations of sound generation by circular cylinder,noise around circular cylinder attached with splitter plate and noise around NACA0012 airfoil,the paper proves that GILBM method can be well applied to the direct numerical acoustics simulation of complex configuration in non-uniform meshes and provides a certain theoretical basis for noise reduction research.Results show that vortices shed alternately from the top and bottom sides of the cylinder into the wake which produces the sound waves,and the directivity of the noise from circular cylinder shows a dipole pattern.For cylinders in different incoming velocity flows,the sound pressure conforms to the linear theory and shows the Doppler effect.When spiltter plate is attached to the trailing edge of cylinder,the flow characteristics will be affected and the intensity of the vortex will be suppressed to a certain extent.As a result,the noise generated by the cylinder will be reduced,noise reduction is most obvious when the length of the splitter plate is l/d=1.For the NACA0012 airfoil noise simulation,the results show that the directivity of the sound field exhibits a liftdipolar form.As the angle of attack increases,the noise intensity increases,and the sound wave contains higher-order harmonics at a certain angle of attack.