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

热对流描述了由于热梯度引起的流体运动。对于足够大的梯度，流动是湍流的，即在空间和时间上是混沌的，并且在多个长度尺度上是自相似的。热对流在自然界和工业中的各种传热过程中起着重要作用。实验研究通常是用一种被限制在下面的暖板和上面的冷板之间的流体进行的。靠近顶板和底板，存在热边界层，冷量和热量从热边界层中释放出来（羽流）。这些羽流由于其浮力而驱动流体运动。大多数地球物理和天体物理对流系统都是旋转的，发生的科里奥利力和向心力对流体流动有很大的影响，从而对热传输产生影响。实验和模拟都表明，由于旋转，在热边界层附近形成涡流。在这些涡流中，发生Ekman泵送，其将热（冷）流体从底部（顶部）热边界层深输送到本体中，从而增强热输送。关于理论预测，这种机制是特别有效的热边界层和动力学边界层的大小相等时。由于普朗特数的变化也会改变两个边界层之间的比率，因此期望找到热传输变得最大的某个普朗特数。这一预测是基于计算机模拟，但迄今为止还没有在实验中观察到。我想通过拟议的项目来缩小这一差距。利用高压气体装置和可填充各种液体的对流装置，我想用0.7到350之间的不同普朗特数进行实验。

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.