CFD Analysis of the American Challenger Rocket Car 2006-01-0809

This paper details a computational fluid dynamics (CFD) analysis of the American Challenger car, a rocket-powered vehicle, under development by Bill Fredrick, which is intended to set a new world land speed record. Two different vehicle configurations were analyzed in order to evaluate lift, drag, and moment characteristics at various conditions. The geometries differed in the design of the rear strut and wheel housing; one having a diamond-shape profile, and the other a bi-convex, double-cusp shape. Steady-state simulations of the entire vehicle were performed at 4,000 ft elevation conditions, with and without active propulsion, and at varying vehicle Mach numbers: 0.6, 0.8, 0.95, and 1.05. The computations were performed on an unstructured mesh of approximately 8.2 million computational cells, which includes half of the vehicle with a symmetry plane (thus, sideslip is not taken into consideration). In all cases, velocities were imposed at the ground to match the speed of the free stream, and corresponding angular velocities were applied to the wheels. The full Reynolds-Averaged Navier-Stokes (RANS) equations were solved, utilizing Metacomp Technologies’ realizable k-epsilon turbulence closure with an advanced wall function. All computations were performed using the CFD++ solver. Results indicate stable flow and nose-down moments with active propulsion under all speed conditions. However, the lower speed cases with no propulsion indicate unsteady flow and nose-up moments. Under the latter circumstances the diamond-shape geometry yields higher lift, drag, and pitching moment than the bi-convex topology does. The latter topology also induces lower amplitude but higher frequency oscillations relative to the diamond-shape geometry, due to differing shock structures and separation bubbles on the struts.