Mixed insulating and conducting thermal boundary conditions in Rayleigh–Bénard convection



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Journal of Fluid Mechanics


A series of direct numerical simulations of Rayleigh–Bénard convection, the flow in a fluid layer heated from below and cooled from above, were conducted to investigate the effect of mixed insulating and conducting boundary conditions on convective flows. Rayleigh numbers between and were considered, for Prandtl numbers and . The bottom plate was divided into patterns of conducting and insulating stripes. The size ratio between these stripes was fixed to unity and the total number of stripes was varied. Global quantities, such as the heat transport and average bulk temperature, and local quantities, such as the temperature just below the insulating boundary wall, were investigated. For the case with the top boundary divided into two halves, one conducting and one insulating, the heat transfer was found to be approximately two-thirds of that for the fully conducting case. Increasing the pattern frequency increased the heat transfer, which asymptotically approached the fully conducting case, even if only half of the surface is conducting. Fourier analysis of the temperature field revealed that the imprinted pattern of the plates is diffused in the thermal boundary layers, and cannot be detected in the bulk. With conducting–insulating patterns on both plates, the trends previously described were similar; however, the half-and-half division led to a heat transfer of about a half of that for the fully conducting case instead of two-thirds. The effect of the ratio of conducting and insulating areas was also analysed, and it was found that, even for systems with a top plate with only 25 % conducting surface, heat transport of 60 % of the fully conducting case can be seen. Changing the one-dimensional stripe pattern to a two-dimensional chequerboard tessellation does not result in a significantly different response of the system.




Copyright 2017 Journal of fluid mechanics. This is a pre-print version of a published paper that is available at :https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/mixed-insulating-and-conducting-thermal-boundary-conditions-in-rayleighbenard-convection/BE6B1738E0575AF7DF468CC9FDA96106 Recommended citation: Bakhuis, Dennis, Rodolfo Ostilla-Mónico, Erwin P. Van Der Poel, Roberto Verzicco, and Detlef Lohse. "Mixed insulating and conducting thermal boundary conditions in Rayleigh–Bénard convection." Journal of fluid mechanics 835 (2018): 491-511.doi:10.1017/jfm.2017.737. This item has been deposited in accordance with publisher copyright and licensing terms and with the author's permission.