Research On LES Subgrid-scale Models And Wall Functions For Sedan Exterior Aerodynamic Noise

Aerodynamic noise is an important sound source of the sedan at high speed,significantly affecting driving comfort. At present, there are many kinds of methods to studyaerodynamic noise. The CFD method has been applied to aerodynamic noise prediction.However, improving the prediction accuracy becomes the key research topic. Therefore,aiming at the aerodynamic noise of the rearview mirror and A column side window region,this thesis investigates the influence of different subgrid-scale models and wall function onsimulation accuracy.CFD method was used to investigate the aerodynamic noise of the rearview mirror andA column side window region, and the results were compared with wind tunnel experiment.In CFD method, the open source computational fluid software OpenFOAM platform wasused to build DSLM and WALEM subgrid-scale models on basis of its own SLM. LESmethods of the SGS (SLM, DSLM and WALEM) were implemented and wall functionkqRWallFunction was added.Through the research of the flow field on a simple2D circular cylinder and a simple3Drearview mirror，the accomplished LES method is verified mainly from two aspects ofqualitative and quantitative, including vortex structure, velocity field, pressure field andsound pressure level. By comparison, wall function kqRWallFunction can improve obviouslythe simulation accuracy, and the subgrid-scale models (SLM and DSLM) have highprecision and good applicability.LES method of SLM and DSLM was selected and the wall function kqRWallFunctionwas added to simulate the exterior field of the full vehicle model. First of all, to solve thecoarse grid computational domain without boundary layers, the information of the formerflow field is mapped to the dense grid flow field with boundary layers. The former flow fieldinformation serves as the initial condition of the latter, and the same method was used to solve continually. The key flow field information of the mirror and side window is acquired,such as the velocity field, the pressure field, the distribution of the turbulent flow a nd soundfield.The mechanism of the aerodynamic noise of the sedan rearview mirror and A pillar wasconcluded. On one hand, after passing the rearview mirror, the airflow forms the turbulencevortex. The continually shedding turbulence vortex crashes the side window to form theaerodynamic noise. On the other hand, the airflow separates after passing the A pillar and theseparation airflow attaching to the side window can also form the aerodynamic noise. Itplays an important role in the design of the sedan. It provides the basis for the engineeringapplication of LES method in the aerodynamic noise simulation.