Controlling secondary flow in Taylor–Couette turbulence through spanwise-varying roughness. (25th January 2020)

• Record Type: Journal Article
• Authors: Bakhuis, Dennis; Ezeta, Rodrigo; Berghout, Pieter; Bullee, Pim A.; Tai, Dominic; Chung, Daniel; Verzicco, Roberto; Lohse, Detlef; Huisman, Sander G.; Sun, Chao
• Is Part Of: Journal of fluid mechanics. Volume 883(2020)
• Publication Date: 2020-01-25
• Subjects: rotating turbulence, -- turbulent boundary layers, -- Taylor–Couette flow; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2019.878
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Abstract : Highly turbulent Taylor–Couette flow with spanwise-varying roughness is investigated experimentally and numerically (direct numerical simulations with an immersed boundary method) to determine the effects of the spacing and spanwise width $s$ of the spanwise-varying roughness on the total drag and on the flow structures. We apply sandgrain roughness, in the form of alternating rough and smooth bands to the inner cylinder. Numerically, the Taylor number is $O(10^{9})$ and the roughness width is varied in the range $0.47\leqslant \tilde{s}=s/d\leqslant 1.23$, where $d$ is the gap width. Experimentally, we explore $Ta=O(10^{12})$ and $0.61\leqslant \tilde{s}\leqslant 3.74$ . For both approaches the radius ratio is fixed at $\unicode[STIX]{x1D702}=r_{i}/r_{o}=0.716$, with $r_{i}$ and $r_{o}$ the radius of the inner and outer cylinder respectively. We present how the global transport properties and the local flow structures depend on the boundary conditions set by the roughness spacing $\tilde{s}$ . Both numerically and experimentally, we find a maximum in the angular momentum transport as a function of $\tilde{s}$ . This can be attributed to the re-arrangement of the large-scale structures triggered by the presence of the rough stripes, leading to correspondingly large-scale turbulent vortices.