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Pumping or drag reduction?

Published online by Cambridge University Press:  10 September 2009

JÉRÔME HŒPFFNER*
Affiliation:
Department of Mechanical Engineering, Keio University, Yokohama 223-8522, Japan
KOJI FUKAGATA
Affiliation:
Department of Mechanical Engineering, Keio University, Yokohama 223-8522, Japan
*
†Email address for correspondence: jerome@fukagata.mech.keio.ac.jp
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Abstract

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Two types of wall actuation in channel flow are considered: travelling waves of wall deformation (peristalsis) and travelling waves of blowing and suction. The flow response and its mechanisms are analysed using nonlinear and weakly nonlinear computations. We show that both actuations induce a flux in the channel in the absence of an imposed pressure gradient and can thus be characterized as pumping. In the context of flow control, pumping and drag reduction are strongly connected, and we seek to define them properly based on these two actuation examples. Movies showing the flow motion for the two types of actuation are available with the online version of this paper (journals.cambridge.org/FLM).

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Type
Papers
Copyright
Copyright © Cambridge University Press 2009

Hoepffner and Fukagata supplementary movie

Movie 1. Peristalsis at Reynolds 100 and wavelength 2π for three constrictions φ. The pressure field is shown by the colormap, the streamwise velocity is shown by velocity profiles. Passive particles tracers are present to emphasize the details of the flow motion. The wall deformation in the form of a traveling wave induces a flow from regions being constricted to regions being expanded: both forward and backward. The backward flow takes place in a constricted region, where viscosity opposes the motion. This results in pumping in the direction of the wave.

Download Hoepffner and Fukagata supplementary movie(Video)
Video 9.4 MB

Hoepffner and Fukagata supplementary movie

Movie 2. Blowing and suction at wave amplitude φ=0.2 and wavelength 2π for three Reynolds numbers. The traveling wave of blowing and suction entrains particles in rotating trajectories. The backward part of this rotation takes place away from the wall, whereas the forward part of the rotation takes place close to the wall where viscosity opposes the motion. This results in pumping in the direction opposite to the wave.

Download Hoepffner and Fukagata supplementary movie(Video)
Video 8.9 MB