Abstract
A novel flow control method, by adding a closed flexible coating to a rigid body, has been proven a significant drag reduction in the two-dimensional flow in a soap film tunnel (Phys. Rev. Lett., vol. 125(3), 2020, pp. 034502). In the present study, we extend this method to three-dimensional rigid bluff body (a flat plate) flows through wind tunnel experiments. The Reynolds number (Re) based on the free-stream velocity (U∞) and the flat plate width is 24000. The length ratio of the flexible membrane (Lr) is in the range of 1.33∼3.23, and Lr = 1 represents a bare plate scenario. The effect of the length ratio on the drag of the rigid-flexible coupling system is discussed. It is found that the mean drag varies nonmonotonically to the length ratio. Benefiting from the closed flexible membrane, the coupled rigid-flexible system achieves a significant drag reduction in three-dimensional flows. The maximum drag reduction of approximately 19.1% is observed under specific conditions (Lr = 2.43). The flexible membrane self-adapts to a more streamlined shape and substantially changes the flow structures behind the plate. Controlled by the flexible membrane at Lr = 2.43, the flow separation is delayed, and the wake region changes to a narrow and shorter region, resulting in a significant drag reduction. The preliminary results obtained in the present study may shed some light on the closed flexible coating flow control method towards some real-life situations and potential applications.
