This study analyzes the flow around a circular cylinder when a dielectric barrier discharge (DBD) plasma actuator is mounted on the cylinder surface. The experiments are mainly performed at Re = 26500. Flow visualization, surface pressures, and wake velocity measurements are performed for the on and off modes of the plasma (pulse modulated drive). The results indicate that the wake expansion and the length of the cavity region significantly change depending on the actuator location, duty ratio and modulation frequency. When the actuator is located close to the separation point and is driven at the Karman vortex shedding frequency (St = 0.19) with the symmetric actuation mode or at St = 0.38 with the asymmetric actuation mode, the vortex shedding is amplified and the surface pressure behind the cylinder decreases; consequently, the pressure drag increases. On the other hand, at a higher modulation frequency (St ≧1), the vortex shedding process is weakened and the wake turbulence is suppressed; consequently, the drag is reduced to 80% of the non-excited case.
Flow characteristics of a two-dimensional jet with side walls have been studied experimentally. Three kinds of cylindrical walls and a flat wall were provided as the side walls, and they were combined and attached to a nozzle. Nine types of side wall conditions were investigated. Velocity was measured by a hot-wire probe and the separation point was measured by a Pitot tube. Mean velocity profiles, the growth of the jet half-width, the decay of jet maximum velocity, and the attachment distance were clarified. When cylindrical walls with different radii are installed, the flow pattern changes markedly depending on the velocity of the jet. A striking increase in the jet half-width is related to the separation of flow from the smaller cylindrical wall just behind the nozzle.
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