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The instability of streaks and the generation mechanism of streamwise vorticity in near-wall turbulence

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Kawahara, Genta and Jiménez, J. and Uhlmann, Markus and Pinelli, Alfredo (2000) The instability of streaks and the generation mechanism of streamwise vorticity in near-wall turbulence. Transactions of the Japan Society of Mechanical Engineers. B, 66 (642). pp. 383-391. ISSN 0387-5016

Official URL: http://sciencelinks.jp/j-east/article/200011/000020001100A0299316.php



Abstract

The linear stability analysis has been performed at Re.TAU.=180 for a turbulent-channel-type base flow with a periodic undulation in the spanwise direction in order to elucidate the generation mechanism of streamwise vorticity through the instability of streaks in near-wall turbulence. It is found that there appear three different instability modes depending on the spanwise wavenumber of streaks. In the case of the streak with around 100 wall-unit spanwise wavelength its critical velocity amplitude lies at .DELTA.Uc+.IMAGE.3, above which streaky flow is unstable to an infinitesimal sinuous disturbance, i. e. a bending mode along the streamwise direction. The instability is identified to originate from inflection points, i. e. wake-like instability, in the spanwise variation of the streaky flow. In this case, unstable eigenmodes take a form that is inclined towards the streamwise direction from the wall-normal direction, and they directly induce the streamwise vorticity on low- and high-speed streaks. In addition, the streamwise vorticity is secondarily produced pricipally through tilting of the wall-normal disturbance vorticity by the base flow shear across the wall-normal direction.


Item Type:Article
Subjects:Sciences > Physics
ID Code:22081
Deposited On:25 Jun 2013 11:41
Last Modified:12 Dec 2018 15:07

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