Energy production and self-sustained turbulence at the Kolmogorov scale in Couette flow. (17th November 2017)

• Record Type: Journal Article
• Authors: Yang, Qiang; Willis, Ashley P.; Hwang, Yongyun
• Is Part Of: Journal of fluid mechanics. Volume 834(2018)
• Page Start: 531
• Page End: 554
• Publication Date: 2017-11-17
• Subjects: turbulence simulation, -- turbulence theory, -- turbulent flows; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2017.704
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Several recent studies have reported that there exists a self-similar form of invariant solutions down to the Kolmogorov microscale in the bulk region of turbulent Couette flow. While their role in a fully developed turbulent flow is yet to be identified, here we report that there exists a related mechanism of turbulence production at the Kolmogorov microscale in the bulk region of turbulent Couette flow by performing a set of minimal-span direct numerical simulations up to friction Reynolds number $Re_{\unicode[STIX]{x1D70F}}\simeq 800$ . This mechanism is found to essentially originate from the non-zero mean shear in the bulk region of the Couette flow, and involves eddy turn-over dynamics remarkably similar to the so-called self-sustaining process (SSP) and/or vortex–wave interaction (VWI). A numerical experiment that removes all other motions except in the core region is also performed, which demonstrates that the eddies at a given wall-normal location in the bulk region are sustained in the absence of other motions at different wall-normal locations. It is proposed that the self-sustaining eddies at the Kolmogorov microscale correspond to those in uniform shear turbulence at transitional Reynolds numbers, and a quantitative comparison between the eddies in uniform shear and near-wall turbulence is subsequently made. Finally, it is shown that turbulence production by the self-sustaining eddies at the Kolmogorov microscale is much smaller than that of full-scale simulations, and that the difference between the two increases with Reynolds number.