WAKE MEASUREMENT OF A SIMPLE BLUFF BODY WITH VARYING REAR END DESIGN AND CLOSE PROXIMITY TO GROUND

The flow field around simplified bluff bodies constitutes a classic area within vehicle aerodynamics. In this study we are looking at the wake flow of a vehicle-like simplified model with and without a rear open diffuser in close proximity to ground. The measurements were done with stationary ground simulation in the L2 scale model wind tunnel at Chalmers University of Technology in Gothenburg, Sweden. The wake flow was measured with a 12-hole omniprobe that has a spherical probe head of 6.35 mm. The purpose was to test how well this probe suits wake measurements of small vehicle-like bodies in ground proximity. The testing was done to a boat tailed/fast back model of small scale. Reynolds number for the experiments was about 1,01 million based on the model length and will be considered low compared to a full scale passenger vehicle. Since the main objective was to test the measurement method, the result is still valid. Measurements are compared to simulations done in the commercial CFD code Fluent. The task was to study the rear end of a simplified bluff body by measuring the close wake of a model with and without a diffuser. A diffuser reduces the drag of this model significantly, and the flow measurements show the difference in wake size and vortex formations