The effect of Prandtl number on turbulent sheared thermal convection. (15th January 2021)

• Record Type: Journal Article
• Authors: Blass, Alexander; Tabak, Pier; Verzicco, Roberto; Stevens, Richard J.A.M.; Lohse, Detlef
• Is Part Of: Journal of fluid mechanics. Volume 910(2021)
• Publication Date: 2021-01-15
• Subjects: turbulent convection, -- Bénard convection, -- atmospheric flows; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2020.1019
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : In turbulent wall sheared thermal convection, there are three different flow regimes, depending on the relative relevance of thermal forcing and wall shear. In this paper, we report the results of direct numerical simulations of such sheared Rayleigh–Bénard convection, at fixed Rayleigh number $Ra=10^{6}$, varying the wall Reynolds number in the range $0 \leqslant Re_w \leqslant 4000$ and Prandtl number $0.22 \leqslant Pr \leqslant 4.6$, extending our prior work by Blass et al. ( J. Fluid Mech., vol. 897, 2020, A22), where $Pr$ was kept constant at unity and the thermal forcing ( $Ra$ ) varied. We cover a wide span of bulk Richardson numbers $0.014 \leqslant Ri \leqslant 100$ and show that the Prandtl number strongly influences the morphology and dynamics of the flow structures. In particular, at fixed $Ra$ and $Re_w$, a high Prandtl number causes stronger momentum transport from the walls and therefore yields a greater impact of the wall shear on the flow structures, resulting in an increased effect of $Re_w$ on the Nusselt number. Furthermore, we analyse the thermal and kinetic boundary layer thicknesses and relate their behaviour to the resulting flow regimes. For the largest shear rates and $Pr$ numbers, we observe the emergence of a Prandtl–von Kármán log layer, signalling the onset of turbulent dynamics in the boundary layer.