Flow control over tandem cylinders using plasma actuators

Abstract

The flow over two circular cylinders, arranged in a tandem setup, is controlled with the help of dielectric-barrier-discharge (DBD) plasma actuators mounted on the upstream cylinder at a Reynolds number (Re) of 4700. The plasma actuators are mounted at ±80∘ from the forward stagnation point of the upstream cylinder. Three tandem configurations are tested, where the distance, L, by which the cylinder centers are separated are fixed at 3, 4, and 5 cylinder diameters (D). For each configuration, the plasma actuators are operated at two distinct blowing ratios (BR) of 0.8 and 1.4, which are named as the low-power and high-power forcing cases, respectively. Results include static-pressure measurements on the downstream cylinder and wake surveys using Particle Image Velocimetry (PIV). High-power forcing changes the flow pattern in the L=3D upstream wake from reattached to co-shedding flow, enabling alternating vortex shedding to occur between the tandem cylinders. High-power forcing also significantly weakens vortex shedding from the upstream cylinder for L=4D and L=5D. This weakening is manifested through 39.27% and 35.32% reductions in the total area of vorticity contours for L=4D and L=5D, respectively. However, the effect of this cancellation is most prominent on the downstream cylinder when the separation distance is L/D=3. During forcing with BR = 1.4, the static pressure on the downstream cylinder resembles that of a flow over a regular cylinder for all the cases tested. Hence, at this blowing ratio, the wake signature of the upstream cylinder is severely diminished, by delaying the shear-layer separation point. During forcing with BR = 0.8, no significant effect on the downstream cylinder is observed.