NUMERICAL SIMULATION OF UNSTEADY THREEDIMENSIONAL DETACHED FLOW AROUND THE REFERENCE AHMED CAR MODEL

Abstract

Listen

Translate article

For the numerical simulation of the flow around simplified Ahmed Car type vehicle the Reynolds averaged Navier-Stokes equations of a viscous incompressible fluid were applied. To close the system of equations, the Shear Stress Transport (SST) turbulence model was used. The numerical solution of the governing equations was obtained by the control volume method. The numerical technique is implemented in program-methodical ware, written in the Fortran language. The computational domain around the Ahmed Car body is divided into control volumes by an unstructured hexahedral mesh consisting of 3.5 million cells. Calculations of two variants of the reference geometry - with the rear slant angle of 25° and 35° were carried out. The Reynolds number based on model length was equal to 2.6 million. The calculation results were visualized, analyzed and compared with results of other authors. The distributions of the velocity modulus, the pressure and the streamlines in the Ahmed Car symmetry plane, the distribution of the pressure and friction coefficients along the model surface, the distribution of the velocity vector in the cross section behind the Ahmed Car body were represented. The visualization of the return-flow region behind the rear surface of the model and the trailing vortex obtained by the isosurface of the velocity invariant Q was performed. For comparison, the results of other authors are presented: the velocity distribution in the longitudinal section and the pressure distribution along the Ahmed Car from the work of Banga S., the distribution of the velocity vectors in the cross section behind the Ahmed Car body from the works of Minguez M. and Lienhart H. The simulation results completely reproduce all known features of the flow structure around the Ahmed Car body. The aerodynamic characteristics of Ahmed Car were obtained. The drag coefficient was 0.255 and 0.268 for the rear slant angle of 25° and 35° respectively, which agrees well with the results of other numerical and experimental studies. The obtained results indicate the practical applicability of the chosen method and the developed program-methodical ware for the tasks of the ground vehicle aerodynamics.