Dimples for Skin-Friction Drag Reduction: Status and Perspectives

Abstract

Dimples are small concavities imprinted on a flat surface, known to affect heat transfer and also flow separation and aerodynamic drag on bluff bodies when acting as a standard roughness. Recently, dimples have been proposed as a roughness pattern that is capable of reducing the turbulent drag of a flat plate by providing a reduction of skin friction that compensates the dimple-induced pressure drag and leads to a global benefit. The question whether dimples do actually work to reduce friction drag is still unsettled. In this paper, we provide a comprehensive review of the available information, touching upon the many parameters that characterize the problem. A number of reasons that contribute to explaining the contrasting literature information are discussed. We also provide guidelines for future studies by highlighting key methodological steps required for a meaningful comparison between a flat and dimpled surface in view of drag reduction.

Features of Controlling the Vortex Flow Structure Using a Pair of Different Geometry Dimples

“…Thus, if we talk about the mechanism of influence of vortex formation in dimples on friction resistances and the intensity of heat transfer in their wake, at the moment there is no unified point of view, which is due to a large number of defining parameters of dimples related to the dynamic characteristics of the inflowing boundary layer, and most importantly, the interpretation of own results [13].…”

Passive flow-field control using dimples for improved aerodynamic flow over a wing

“…Therefore, in the pursuit of improving the aerodynamic performance of lifting surfaces, passive control methods are preferred. These passive techniques are utilized to influence stall phenomena or delaying the flow separation without the need for external energy consumption 6 .…”