Research On Computational Aeroacoustics Of Air Flow Around An Airfoil Based On LBM

The wing part is an important source of noise for passenger airliners.When air flows around wings,it produces separated bubbles or turbulence at the tail,and then forms noise.Therefore,it is of great engineering significance to study the aerodynamic noise yielded by wings.Compared with classical CAA method,the lattice Boltzmann method has advantages of clear process,easy boundary treatment,and et al.So,it has good prospects in computational aeroacoustics.Compressible lattice Boltzmann method is used to research the simulation of turbulence noise at moderate Reynolds number and Mach number.In this paper,compressible LBM model is analyzed and deduced.The Maxwell function is replaced by a circular function with additional degrees of freedom,so that the Boltzmann equation of BGK type can recover the macroscopic governing equations.According to the idea of LBM,the velocity is discretized into limited directions,the first-order Euler forward scheme is adopted to discretize time and the FVM method is taken to discretize space.At solid non-slip wall,the non-equilibrium extrapolation method is carried out.For the non-reflective far field boundary,a target flow function is added in the LBM governing equations to suppress non-physical disturbance.The sound field is obtained by calculating the difference between the present relative pressure value and the mean value of a total certain number steps after flow field reaches a steady state.According to the proposed method,Gauss pulse is firstly simulated.Cloud map and wave curve of sound pressure are plotted to verify the effectiveness of this method.Furthermore,effects of different Reynolds number and absorption coefficient on the sound pressure are compared.Then,the flow around a circular cylinder is simulated.Lift/drag coefficient curve,sound pressure distribution cloud map and wave curve of test points are obtained.Finally,airflow around an airfoil at different Mach numbers is calculated.The surface pressure/friction coefficient curve is acquired,sound pressure distribution cloud map and wave curve of test points are also displayed in the paper.Results of Gauss pulse simulation are close to analytical solutions.With the increase of Reynolds number,influence on the sound pressure decreases.The bigger absorption coefficient,the better the absorption is.Sound field of the flow around a cylinder and an airfoil can be calculated correctly,and the sound pressure wave at test points is very stable.