A Computational and Experimental Analysis of the Flow Around a Blunt-Base Vehicle 2005-01-3626
This paper describes the results of experiments that were performed using a Ground Research Vehicle (GRV) at the National Aeronautics and Space Administration's (NASA) Dryden Flight Research Center in Edwards, CA and a comparison with computational results. The GRV is a modified 1984 General Motors (GMC) van and measures 40 feet long and 9 feet high, with a base area of 83 by 83, and it weighs 10260 lbs and holds a crew of up to three. Air data is measured from a nose-boom, 2 global positioning (GPS) units, and an absolute Honeywell Pressure Transducer with 4 Electronic Signal Processor (ESP) scanners and 64 surface pressure ports. This allows for detailed measurements of the surface pressure profiles around the vehicle. The total vehicle drag is estimated from coast-down tests, while the pressure component of the drag force may be calculated by integrating the pressure profiles on the front and base of the vehicle. The GRV is a variable-geometry vehicle, and three different configurations were studied experimentally at NASA-Dryden: the vehicle with square corners and the undercarriage both fared and un-fared, and the vehicle with the front edges and corners rounded with the undercarriage covered. For the computational work only the latter two configurations have been studied. Vehicle tests were performed at speeds varying from 40 mph to 80 mph. Both steady-flow and transient simulations were performed using the commercial computational fluid dynamics (CFD) code FLUENT running on SUN workstations. While the results from the steady flow simulations using a two-equation Reynolds averaged Navier-Stokes (RANS) turbulence model matched the experimental measurements of the pressure profiles on the front face of the vehicle well, they did not adequately capture the pressure profile on the base of the vehicle, due to the steady computations inability to capture the periodic vortex shedding. Transient computations using a Large Eddy Simulation (LES) turbulence model provided results in much closer agreement to the experimentally measured pressure profiles, which suggests that transient LES computations should always be performed when simulating drag of tractor-trailers and similar vehicles with blunt bases.