Combined Passive/Active Flow Control of Drag and Lift Forces on a Cylinder in Crossflow Using a Synthetic Jet Actuator and Porous Coatings

Abstract

This paper combines a synthetic jet actuator (SJA) and a leeward porous coating to alter the aerodynamic forces on a cylinder in crossflow at Re = 4.2 × 104. While SJAs and porous coatings are known to be effective flow control methods in isolation, their combined effect has not been studied. A 2D numerical model was created of a cylinder with a SJA at 90° and 100° leeward porous coating. The model was validated using accompanying water tunnel tests. The combined model was tested for dimensionless frequencies 0.15 f+ 4 and compared to reference models. For f+ 1, using only the SJA increases the cylinder drag coefficient (Cd). Combining a porous coating with the SJA in that regime lowers the Cd values by 15–21%, and causes an overall reduction in Cd compared to the smooth cylinder baseline case. However, using only the porous coating causes a superior 35% reduction in Cd. For f+> 1, the combined SJA and porous coating configuration did not differ from the SJA only configuration, achieving the largest drag reduction of 45% at f+ = 4. The flow control mechanisms of the SJA and porous coating do not combine constructively in this current setup. However, the porous coating is beneficial for f+ 1, causing an overall drag reduction even when the active SJA tends to increase drag.

Keywords

• drag reduction
• oscillating lift
• porous media flow
• vortex shedding
• synthetic jet
• experimental fluid dynamics