NUMERICAL INVESTIGATION OF THE EFFECTS OF BASE SLANT ON THE WAKE PATTERN AND DRAG OF 3-DIMENSIONAL BLUFF-BODIES WITH A REAR BLUNT END

A computational model has been developed to help the automotive design engineer to optimize the body shape with minimum wind tunnel testing. Unsteady, Reynolds-averaged, Navier-Stokes equations have been solved numerically by a finite-volume method and have been applied to study the flow around Ahmed's vehicle-like body. The standard k-epsilon mode l has been employed to model the turbulence in the flow. The finite vo lume equations have been formulated in a strong conservative form on a three-dimensional, unstructured grid system. The resulting equations have been solved then by an implicit, time marching pressure-correctio n based algorithm. The steady state solution has been obtained by taki ng sufficient time steps until the flow field ceases to change with ti me within a prescribed tolerance. For the pressure-correction equation , a preconditioned conjugate gradient method has been employed to obta in the solution. Most of the essential features of the flow field arou nd a bluff body in ground proximity, such as the formation of trailing vortices and the reverse flow region resulting from separation, could be well predicted. In addition, the variation of the drag coefficient with the back slant angle agreed reasonably well with the experimenta lly observed values.