Flow Visualization and Drag Measurement of a Circular Cylinder in Compressible Flow at Reynolds Number Between 1000 and 5000

In this study, a compressible low-Reynolds number flow over a circular cylinder was investigated by schlieren visualization and the force measurement. A Reynolds number based on freestream quantities and a diameter of a cylinder is set to be 1000 ≤ Re ≤ 5000 and a Mach number is set to be 0.1 ≤ M ≤ 0.5 by using the low-pressure wind tunnel. From the schlieren visualization, frequency of the vortex shedding was obtained by performing frequency analysis on the time series schlieren images. Near wake structure by the circular cylinder is measured by time-averaged schlieren image. Even though M is less than 0.5, the structure of the flow fields changes depending on M. The effect of M on the scale of wake structure depends on Re. Under the condition at Re of 1000–3000, the scale becomes large as M increases more than 0.2. On the other hand, under the condition that Re is 4000–5000, it becomes small as M increase 0.3 or more St is revealed to be decrease for Re of 2000–3000 with increasing M, and St increases at Re of 4000–5000. From the force measurement, drag coefficient (Cd) and pressure distribution on a circular cylinder (Cp) obtained. The effect of M on Cd does not depend on Re, and Cd also increases as M increases. The effect of Re on Cd is also observed that Cd increases as Re increases and this trend doesn’t depend on M. The Cp decrease with Re increase. The M effect on Cp is that the range of Cp is enlarged with M increase.

Drag reduction due to recirculating bubble control using plasma actuator on a squareback model

Flow control on a squareback object which resembles many engineering related objects is believed to be highly beneficial. One of the flow characteristics behind the object, recirculating bubble, is known to play significant role in pressure distribution. Meanwhile, plasma actuator implementation on such object is still underdeveloped in application basis. This paper focuses on acquiring a deeper understanding of plasma actuator effect on flow phenomenon behind a squareback object, especially on its application to recirculating bubble control in order to reduce drag. The experiment was divided into drag measurement experiment and visualization experiment. The drag measurement result shows that plasma actuator succeeded on reducing drag up to 15.36% in the lowest Reynolds number. Meanwhile, the visualization experiment shows that plasma actuator has shifted the recirculating bubble position to be closer to the object’s wall.