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On Permeability and Roughness Effects in Flow Past a Row of Circular Cylinders Arranged Along the Centerline of a Straight Flume

Author(s): Satoshi Yokojima, Ryosuke Asaoka, Koudai Yoshino, Hiroshi Noda, Takashi Miyahara

Linked Author(s): Satoshi Yokojima

Keywords: Permeability effect, roughness effect, a row of circular cylinders, drag, two-dimensional high-fidelity numerical experiment


The presence of a row of circular cylinders along the centerline in a flume gives a significant drag to the flow. The row can be seen macroscopically as a porous flat plate having both permeability and roughness effects, and the flow over semiannular stripe roughness elements is the system obtained by removing only the permeability from the flow past the cylinders. In the present study, these flows have been studied comparatively by a two-dimensional high-fidelity numerical experiment to elucidate the impacts of the permeability and roughness on the flow resistance. The drag on the row of cylinders is found to be roughly one order of magnitude higher than that over the roughness elements. In other words, the permeability causes much more resistance to the flow than the roughness. The importance of the former tends to be decreased with the decrease in the number of cylinders (i.e. increase in the plate porosity). Visualization of the instantaneous flow fields reveals the presence of large scale vortices in both types of the flows, and the intensity of the vortices is significantly enhanced by the boundary permeability. This then promotes fluid mixing and associated momentum exchange over the whole cross section, and increases the resistance to the flow. (2603, 72, 354)


Year: 2017

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