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Towards the numerical investigation of rough surfaces in quasi two-dimensional Rayleigh-Benard convection

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The aim of the present work is to investigate numerically the influence of roughness on Rayleigh-Bénard convection in threedimensional rectangular containers in Direct Numerical Simulations (DNS). We seek for a domain that allows a quasi two-dimensional flow even for small Rayleigh numbers, which are preferable due to lower computational costs. It turns out that the influence of the vertical walls is not negligible and leads even to stationary flows at rather large Rayleigh numbers. Therefore, a free-slip condition has been prescribed on two nearby walls and the differences to the no-slip case with increasing Ra are studied. The main idea is, that for low Rayleigh numbers the free-slip walls lead to an already quasi two-dimensional flow, while for very large Rayleigh numbers (as they occur in experiments in similar containers) the differences in the boundary conditions are negligible when investigating global
quantities like the mean heat flux, since the flow is bulk dominated. The DNS results for no-slip and free-slip boundary conditions are compared with those in the two-dimensional case.

Author(s):

Sebastian Wagner    
German Aerospace Center (DLR)
Germany

Olga Shishkina    
German Aerospace Center (DLR)
Germany