EXPERIMENTAL INVESTIGATION OF UNSTEADY AERODYNAMICS AND FLOW CONTROL FOR FLEXIBLE STRUCTURE

Abstract

Unsteady fluid and structure interactions have many practical applications like revealing the flow phenomenon involved in natural swimmers and fliers' propulsion, exploiting the potential possibilities in energy harvesting, heat transfer augmentations, and the aerodynamic structures' stability. Recently, the effect of elastic structures on aerodynamic characteristics of the bluff bodies and the reconfiguration of the flexible structure under the aerodynamic forces intrigues the aerodynamicists. A few more fields are being explored, like flow control of bridge piers, heat transfer augmentation using pin fins with attached flexible splitter plates, design and development of micro energy harvesters, and flexible flapping wing micro aerial vehicles. The present study explores the behavior of the flexible structure in two aerodynamic applications. Firstly in the bluff body aerodynamics and second in the flapping-wing dynamics. Both the flow applications pose unsteady flow conditions for the flexible structures. The effects of the fluid-structure interactions are reported in the study. Also, a comparison between the rigid and flexible structure has been drawn. Many studies also revealed the flow structures and response of a flexible splitter plate involved in fluid-structure interaction with a circular bluff body. Comparatively, less attention has been imparted to the flexible splitter plate behaviour in the wake of a bluff body with sharp corners and its effect on the flow structure downstream of the body. The impact of the flexibility of the plate on the wake characteristics and the total mean drag of the bluff body has not been studied thoroughly. The present experimental study investigates the effect of length and flexibility of the flexible splitter plate on flow across a square cross-section cylinder. The flow diagnosis techniques like particle image velocimetry (PIV), flow visualization, and hot wire anemometry (HWA) characterize the flow over the square cylinder and control it using the passive methods. The intermediate-range Reynolds numbers are varied from 600 to 2000. Two flow regimes characterize the flow over the cylinder. The first regime is of a fine-scale three-dimensional wake found at Re = 600, where the two-dimensional primary instability loses its strength, and the formation length of the vortices becomes large. For Re > 600, the shear layer transition regime is observed where the vortex formation length decreases monotonically.