On the influence of rotation on turbulent thermal convection for different Prandtl numbers

点击翻译按钮获取中文摘要

Thermal convection describes the motion of a fluid due to a thermal gradient. For sufficiently large gradients, the flow is turbulent, i.e. chaotic in space and time and self-similar over multiple length scales. Thermal convection plays an important role in a large variety of heat transport processes in nature and industry. Experimental investigations are usually done with a fluid that is confined between a warm plate from below and a cold plate from above. Close to the top and bottom plates, thermal boundary layers exist out of which cold and hot volumes are released (plumes). These plumes drive the fluid motion due to their buoyancy.Most geo- and astrophysical convection systems are rotating and the occurring Coriolis and centripetal forces have a strong influence on the fluid flow and thus on the heat transport. It was shown in experiments as well as in simulations, that due to rotation vortices form close to the thermal boundary layers. In these vortices, Ekman pumping takes place that transports hot (cold) fluid from the bottom (top) thermal boundary layer deep into the bulk and thus enhances the heat transport. Regarding theoretical predictions, this mechanism is especially effective when the thermal and kinetic boundary layers are of equal size. Since a change of the Prandtl number also changes the ratio between both boundary layers, it is expected to find a certain Prandtl number for which the heat transport becomes maximal. This prediction is based on computer simulations but was so far not observed in experiments. I would like to close this gap with the proposed project. With a high-pressure gas apparatus and a convection apparatus that can be filled with various liquids, I would like to conduct experiments with different Prandtl numbers between 0.7 and 350.