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

热对流描述了由于温度梯度引起的流体的运动。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，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热传递过程中起着重要的作用。实验研究通常是用一种流体进行的，这种流体被限制在从下往下的温板和从上方往上的冷板之间。在靠近顶板和底板的地方，存在热边界层，从中释放出冷量和热量(羽流)。这些羽流通过浮力驱动流体运动。大多数地球和天体对流系统都是旋转的，产生的科里奥利力和向心力对流体流动有很强的影响，从而对热量传输有很大影响。实验和模拟都表明，在靠近热边界层的地方，由于旋转而形成了旋涡。在这些涡旋中，发生了埃克曼泵送，将热(冷)流体从底部(顶部)热边界层输送到主体深处，从而增强了热量传输。关于理论预测，当热力边界层和动能边界层大小相等时，这种机制尤其有效。由于Prandtl数的变化也改变了两个边界层之间的比率，因此有望找到一个特定的Prandtl数，对于该Prandtl数，热量传输变得最大。这一预测是基于计算机模拟，但到目前为止还没有在实验中观察到。我想用拟议的项目来弥合这一差距。有了高压气体装置和可以装满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.