The effects of ground simulation on tractor-trailer combinations

The 9-meter wind tunnel of the National Research Council (NRC) of Canada is equipped with a boundary layer suction system, center belt and wheel rollers to simulate ground motion relative to test articles. Although these systems were originally commissioned for testing of full-scale automotive models, they are appropriately sized for ground simulation with half-scale tractor-trailer combinations. The size of the tunnel presents an opportunity to test half-scale commercial vehicles at full-scale Reynolds numbers with a model that occupies 3% of the test section cross-sectional area. This study looks at the effects of ground simulation on the force and pressure data of a half-scale model with rotating tractor wheels. A series of model changes, typical of a drag reduction program, were undertaken and each configuration was tested with both a fixed floor and with full-ground simulation to evaluate the effects of this technology on the total and incremental drag coefficients. The question was whether ground simulation affected predictions of the drag change due to typical model changes. Effects of the ground simulation were further considered by employing wheel rotation or the center belt alone. This was undertaken to determine whether a simplified ground simulation system would suffice for commercial vehicle testing. Copyright \ua9 2013 SAE International.Peer reviewed: YesNRC publication: Ye