Aerodynamic drag on deformable and active structures in high Reynolds number conditions

Abstract

We explore the effect of topography on the aerodynamic behavior of deformable structures, at high Reynolds numbers. We first introduce a novel mechanism to control the aerodynamic drag on cylinders, in the critical Reynolds number regime. We created both axially grooved and dimpled specimens, comprised of latex membranes stretched over rigid acrylic skeletons. By decreasing the internal pressure of the specimens, the latex stretched inward thus changing the shape of the surface. Using a combination of finite element simulations and precision mechanical experiments, we characterized the relationship between the mechanical deformation in the membrane and pneumatic loading. Wind tunnel experiments were used to explore how changing several geometric parameters, of both grooved and dimpled cylinders, affected the aerodynamic performance. We also used the tunable nature of the specimens to automatically control the dependence of the drag coefficient on the Reynolds number. Additionally, we studied the effect of holes in thin flexible strips at high Reynolds numbers. In this investigation, instead of controlling the deformation of the specimens, we modified the initial geometry by cutting holes in strips and examined the deformation under uniform aerodynamic loading. We used a combined experimental and numerical approach to study the effect of perforation on the drag coefficient. The work presented in this thesis, represents an important first step towards utilizing deformation to control the aerodynamic performance of structures.