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An experiment was conducted to compare the base-drag reduction of a bluff body employing various passive control means. A 1-ft-long bluff-body model with a blunt square base was tested in the Cal Poly 3’ x 4’ ft lowspeed wind tunnel at three forebody surface roughness conditions, namely, 0.5” sandpaper, 1.5” sandpaper, and transverse grid. The experiment measured total drag and base drag coefficient, surface pressure, and trailing-edge boundary-layer velocity profile at ReL = 1.55, 2.92, and 5.82 x 10 5 . To determine the effect of vortex dynamics on base-drag reduction, a phase-averaged base pressure was also measured, using a conditioning hot-wire signal obtained outside the wake flow. Both mean and phase-averaged base-pressure results indicated that when compared to the smooth model, all three forebody surface roughness conditions increase base suction and reduce base drag, with the transverse grid having the largest base drag reduction. The base drag reductions, however, decreased with increasing Reynolds number. Nomenclature |
