This work aims at finding efficient means to reduce skin friction drag in a turbulent boundary layer. The argument on which the study is based is that turbulence exists near a wall because of the presence of an autonomous cycle which is maintained even in the absence of forcing from the free-stream. The central elements of this cycle are the near-wall coherent structures whose dynamics control the turbulence production. It is postulated that an action at the wall capable of disrupting the turbulent wall-cycle can yield a significant skin friction reduction. A model cycle is produced by embedding artificial, large scale streamwise vortices and streaks in a Blasius boundary layer. A control is then conceived, meant to produce an agglomeration of the streaks to hamper the cycle. The action envisaged consists in a movement of the wall, in the form of a spanwise standing or travelling wave of sufficiently long wavelength. The controllers in the present macroscopic simulation are simply cantilever beams whose movement is driven by ceramic piezo-actuators. Piezoelectric fibers realizing the same action (properly rescaled) provide, possibly, the answer to the technological challenge of the integral control of near-wall turbulence.
Active Control of Near-Wall Coherent Structures
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Konieczny, P, Bottaro, A, Monturet, V, & Nogarede, B. "Active Control of Near-Wall Coherent Structures." Proceedings of the ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. Volume 1: Fora, Parts A and B. Montreal, Quebec, Canada. July 14–18, 2002. pp. 1311-1317. ASME. https://doi.org/10.1115/FEDSM2002-31036
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