Programmable Aerodynamic Drag on Active Dimpled Cylinders

This study demonstrates that the aerodynamic drag profile of a patterned deformable cylinder at high Reynolds numbers can be programmed, on demand, by modifying its topography through pneumatic actuation. The samples used in the experiments comprise a rigid tube containing a hexagonal array of holes, over which an elastomeric cylindrical membrane is stretched. Decreasing the internal pressure of the structure causes an inward deflection of the outer membrane over the holes, thereby producing a regular pattern of dimples. The depth of these dimples can be controlled by tuning the pressure differential. The relationship between the mechanical deformation of the membrane and the pneumatic loading is characterized using a combination of finite element simulations and precision mechanical experiments. Wind tunnel experiments are performed to study how both the depth and the diameter of the dimples dictate the aerodynamic performance of the samples in the critical Reynolds number regime. Finally, the tunable nature of the specimens is exploited to automatically control the dependence of the drag coefficient on the Reynolds number, toward targeting predefined drag profiles.