Large Eddy Simultaion Research And Application In Aeroacoustics With High-order Weighted Compact Nonlinear Schemes

The research of multi-scale turbulence problems in aeroacoustics is entering the stage of large eddy simulation,usually with complex geometries and high Reynolds numbers,which require high resolution and efficiency algorithms.This thesis is based on the seventh-order compact schemes,guided by the requirement of airframe noise simulation and reduction study,has developed a suitable method for sub/transonic aeroacoustics prediction,including the high-precision large eddy simulation method,advanced hybrid RANS/LES model,and the acoustic analogy theory.Firstly,a validation study is conducted for the high-precision implicit large eddy simulation method.In order to evaluate the behavior of the implicit large eddy simulation method,a variety of advanced subgrid models are combined for comparison.The results show that the implicit large eddy simulation based on the seventh-order compact scheme performs best.Compared with the explicit model,it has wider range of application towards various types of turbulent flow.Then,based on the high-precision large eddy simulation method and the advanced turbulence model,the hybrid RANS/LES model based on turbulence mixing has been developed.Several key factors’ influence,including the choice of RANS model,LES model and blending function are studied.Combined with the algebraic transition model,the hybrid model is extended to the transitional study,and it is pointed out that the blending function without wall constraint is not suitable for constructing the hybrid transitional model.At the same time,a comparison of simulation in benchmark problems is carried out with the DES methods,and the advantages of the transitional method based on the hybrid model over the DES model are analyzed.The reliability of the hybrid RANS/LES model in turbulence simulation is confirmed.Based on the hybrid RANS/LES model,a CFD+CAA method for airframe noise prediction is constructed in combination with acoustic analogy theory.The reliability of the far-field noise calculation is investigated through a simple sound source theoretical solution,and the capabilities of schemes with different orders are compared for the sound propagation problem.Finally,the single-cylinder radiation noise,turbulent wakes and airfoil wall interaction noise problems are investigated.The results compare well with the experiment data,and the influence of the selection of the sound source surface on the noise directivity results is studied.Finally,the hybrid CFD+CAA method is applied to the research of airframe noise.In terms of the high-speed aeroacoustic noise,the open-cavity noise was studied.The grid convergence study has been carried out,and the results of different types of cavity flow noise are compared.The effect of the serrated wall on the cavity noise suppression is studied.In terms of low-speed flow noise,the high-lift airfoil and landing gear noise studies have further confirmed the high efficiency of the new method in complex flow.Influence of the airfoil trailing edge shape on the flow characteristics and aerodynamic noise results is analyzed,which provides a basis for further noise reduction research.