Generation of zonal flows in convective systems by travelling thermal waves. (23rd February 2021)

• Record Type: Journal Article
• Authors: Reiter, Philipp; Zhang, Xuan; Stepanov, Rodion; Shishkina, Olga
• Is Part Of: Journal of fluid mechanics. Volume 913(2021)
• Publication Date: 2021-02-23
• Subjects: Bénard convection, -- turbulent convection, -- atmospheric flows; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2020.1186
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : This work addresses the effect of travelling thermal waves applied at the fluid layer surface, on the formation of global flow structures in two-dimensional (2-D) and 3-D convective systems. For a broad range of Rayleigh numbers ( $10^3\leq Ra \leq 10^7$ ) and thermal wave frequencies ( $10^{-4}\leq \varOmega \leq 10^{0}$ ), we investigate flows with and without imposed mean temperature gradients. Our results confirm that the travelling thermal waves can cause zonal flows, i.e. strong mean horizontal flows. We show that the zonal flows in diffusion dominated regimes are driven purely by the Reynolds stresses and end up always travelling retrograde. In convection dominated regimes, however, mean flow advection, caused by tilted convection cells, becomes dominant. This generally leads to prograde directed mean zonal flows. By means of direct numerical simulations we validate theoretical predictions made for the diffusion dominated regime. Furthermore, we make use of the linear stability analysis and explain the existence of the tilted convection cell mode. Our extensive 3-D simulations support the results for 2-D flows and thus provide further evidence for the relevance of the findings for geophysical and astrophysical systems.