Effects of boundary variations on Rayleigh-Bénard convection

Bakhuis, D. (2014) Effects of boundary variations on Rayleigh-Bénard convection.

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Abstract:In this numerical study, we looked into effects of different boundary variations on the flow dynamics of Rayleigh-B´enard convection. These simulations were done using finite differences on a Cartesian grid for Ra = 106, 108, P r = 1, 10. By adding locally heated spots, so called hot spots, we tried to simulate roughness elements, and possibly position or influence the large scale circulation. For different configurations of these hot spots, we saw no significant effect on the flow dynamics. From this work we saw no observable proof that hot spots can act as surrogate roughness. The next step was to add physical roughness, by using the immersed boundary method. Again, single and even small sets of roughness elements, which were slightly higher than twice the thermal boundary layer thickness, did not influence the large scale circulation in a reproducible way. Placing periodic 1D and 2D wavy patterns had a significant effect on the heat transfer rate of the system. The last part of this thesis focuses on the distribution of equally sized conducting and insulating areas on the top wall boundary and their effect on the flow quantities. When dividing both areas only in two segments, N u is approximately 2/3 of the homogeneous case. However, by maximizing the number of segments, N u raises to almost the complete homogeneous case. In a spectral analysis, we showed that the distribution of these areas is indistinguishable outside the thermal boundary layer.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:33 physics
Programme:Applied Physics MSc (60436)
Link to this item:http://purl.utwente.nl/essays/66153
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