Energy loss minimizing drag reduction and self-propulsion strategies

Abstract

Boundary layer separation is the principal cause for the relatively large drag force experienced by a bluff body undergoing uniform motion in an otherwise quiescent fluid. Active and passive flow control strategies which effectively suppress or prevent flow separation are of considerable practical importance as they can facilitate drag reduction and efficient propulsion in mechanical systems like underwater robotic and micro air vehicles. In this work we present a comparative investigation of two popular flow control strategies that rely on normal and tangential surface distortions in order to achieve a reduction in the total drag experienced by a translating circular cylinder. The energetic efficiency of the flow control strategies is quantified using the power loss coefficient; a metric of performance that is directly linked to the net power consumption. The efficacy of the tangential and normal surface distortions based flow control strategies is evaluated and compared using the effective reduction in the hydrodynamic forces and net power consumption in the laminar flow regime. Simulations indicate that the tangential boundary motions are slightly more effective than normal distortions in reducing the total drag on circular cylinder.