Browse Publications Technical Papers 2010-01-0512
2010-04-12

The Effect of Base Bleed and Rear Cavities on the Drag of an SUV 2010-01-0512

Two methods of passive flow control were investigated to determine their effectiveness in reducing aerodynamic drag on large Sports Utility Vehicles (SUVs). Passive means of flow control were selected since all active methods require the input of additional energy (e.g., pressurized fluids or electrical energy). The selected methods were base bleed and the use of a rear cavity, and various combinations of these were experimentally tested in full-scale wind tunnels with and without a moving belt/rotating wheel assembly. Aerodynamic drag reduction was accomplished by restructuring the low-pressure wake directly behind the vehicle.
External cavity depths ranging from d/h=0.17 to 0.83 were used, while body cavity depths ranged from d/h=0 to 0.83, where the depth of the cavity d is non-dimensionalized by the height h of the base area. External cavities always resulted in an increase in the drag coefficient, while for body cavities the reduction in drag improved with increasing cavity depth. A maximum drag reduction of -3.3% was achieved.
The base bleed coefficient was varied from Cq=(3-21) x 10-⁴, and various bleed outlet locations in the base area were considered. Bleeding air around the periphery of the base area was found to be the most effective implementation, and depending on the outlet location the drag reduction ranged from -0.3% to -1.1%.

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