A unified view of energetic efficiency in active drag reduction, thrust generation and self-propulsion through a loss coefficient with some applications

• Published in: Journal of fluids and structures 2013-08, Vol.41, p.22-32
• Main Authors: Arakeri, Jaywant H., Shukla, Ratnesh K.
• Format: Article
• Language: English
• Subjects: Bluff body flows; Coefficients; Computational fluid dynamics; Cylinders; Drag; Drag reduction; Fluid flow; Power loss; Self-propulsion; Translating
• ISSN: 0889-9746; 1095-8622
• DOI: 10.1016/j.jfluidstructs.2013.02.005

An analysis of the energy budget for the general case of a body translating in a stationary fluid under the action of an external force is used to define a power loss coefficient. This universal definition of power loss coefficient gives a measure of the energy lost in the wake of the translating body and, in general, is applicable to a variety of flow configurations including active drag reduction, self-propulsion and thrust generation. The utility of the power loss coefficient is demonstrated on a model bluff body flow problem concerning a two-dimensional elliptical cylinder in a uniform cross-flow. The upper and lower boundaries of the elliptic cylinder undergo continuous motion due to a prescribed reflectionally symmetric constant tangential surface velocity. It is shown that a decrease in drag resulting from an increase in the strength of tangential surface velocity leads to an initial reduction and eventual rise in the power loss coefficient. A maximum in energetic efficiency is attained for a drag reducing tangential surface velocity which minimizes the power loss coefficient. The effect of the tangential surface velocity on drag reduction and self-propulsion of both bluff and streamlined bodies is explored through a variation in the thickness ratio (ratio of the minor and major axes) of the elliptical cylinders.