Numerical methods exploration and experimental validation of Ahmed model with consideration of fluid-solid-interaction effect

Fluid-solid interaction (FSI)between the crosswind and the moving vehicle exerts an impact on driving safety.The reliability of the FSI numerical simulation method needs to be verified.Numerical simulation method and wind-tunnel test method are used with an Ahmed model in the research.Arbitrary Lagrange-Euler (ALE)method is applied to the Ahmed model FSI numerical simulation under crosswinds at velocities of 20m/s,25m/s,30m/s,35m/s,and 40m/s.Through comparison between numerical solution of the Ahmed model and experimental results,it can be claimed that the displacement difference is less than 20%.The experimental methods contain pressure and deformation measurements and flow visualization technique (plume-tracer technique and thread-tracer technique).The flow visualization results are com-pared with the numerical results to verify the reliability.After the comparison of the coupled and uncoupled numerical results,it is found that variation in aerodynamic forces is mainly caused by ever-changing topologic structure of vortices.In this paper,it is found that:(1)FSI effect main-ly intensifies the aerodynamic lift force on the vehicle under crosswind condition(especially at a velocity higher than 25m/s).(2)Aerodynamic lift force increase is mainly caused by the topolog-ical change of the separation bubble above the Ahmed body.FSI effect significantly expands the scale of the separation bubble.(3)Under crosswind condition,FSI effect will increase the rolling trend,so the actual vehicle security is lower than the yield of numerical results with FSI effect unconsidered.Therefore,the use of non-coupling calculation results as a design basis is some-what risky.The present study has laid a theoretical foundation for the upcoming research on the two-way FSI effect on vehicle under time-dependent crosswind condition.In short,the work aims to quantify crosswind acceleration effect and fluid-structure interaction effect of aerodynamic force,to provide a method to research the real vehicle crosswind stability in a finer and more precise way, and to provide a reference to simulate the vehicle travelling status more thoroughly.