Lattice Boltzmann Simulations of the Unsteady Flow Behind the Ahmed Body 2008-01-0740

The Ahmed body is a simplified vehicle geometry that results in flow features representative of those found at the rear of most passenger vehicles. By adjusting the rear slant angle, separation can take place at the sharp corner, on the rear slant panel, or not at all. Accurate prediction of the separation and reattachment of the flow is essential in predicting the correct drag trends. This separation and reattachment is known to be a highly unsteady phenomenon. The objective of this study is to evaluate the ability of a lattice Boltzmann based CFD code to predict the correct drag trends and flow structures for the Ahmed body at varying rear slant angles. Component and total drag values show excellent agreement with the original experiments of Ahmed over a wide range of rear slant angles (5 to 35 degrees). Detailed comparisons of the flow field (velocity profiles on the slant, Cp on the body and wake surveys) at rear slant angles of 25 and 35 degrees are made against the LDV experiments of Leinhart et al.