Experimental and Numerical Investigation of Flow Control on Bluff Bodies by Passive Ventilation

In this work, the so-called natural or passive ventilation drag reduction method is investigated experimentally and numerically. Passive ventilation is performed by directly connecting the high pressure region at the front of a body to the lower pressure in the near wake using a venting duct; in this manner, a net mass flux is established within the wake. In particular, in aerodynamic applications it appears suitable to attain a global reduction in the drag of a body moving in a fluid and a reduction in turbulence levels by means of a global modification of the body wake. Velocity field investigations using particle image velocimetry measurements and a Reynolds averaged numerical code are employed at moderately high Reynolds numbers to clarify the effectiveness of drag reduction on a vented bluff body. The numerical and experimental results agree qualitatively, but the amount of reduction for the vented body (about 10%) is underestimated numerically. The effectiveness of drag reduction has been proved both for smooth and rough (single strip) models. Direct balance measurements are used for comparisons.