液态金属热对流典型流动结构实验研究

Experimental investigation on the typical flow structures of liquid metal thermal convection

通过搭建长宽高比为1∶1∶2的实验方腔,系统性地研究低普朗特数(0.03)的镓铟锡合金在有/无磁场作用下所产生的热对流结构。实验中上下铜板的温差由2个恒温水浴来实现,通过在铜板上布置测温探头测量温度,在方腔侧壁布置超声波探头实现对液态金属内部速度分布的测量。实验获得了3种典型的流动结构,无磁场环境下液态金属的流动在空间上呈现大尺度环流,靠近冷热端液态金属的温度无序波动,且速度分布符合热湍流的基本特性,为流动结构Ⅰ。当施加水平磁场,磁场极大地抑制对流运动,出现稳定的单涡胞运动结构,即流动结构Ⅱ和振荡的双涡胞运动结构,即流动结构Ⅲ。随后通过对3个不同测量位置的速度分布进行详细分析,深入解析水平磁场存在下的这2种流动结构的典型特征。

In the present paper, we built a rectangle cell with an aspect ratio of 1∶1∶2, where the height of the cell is two times the width of the cell. The thermal convection of liquid Galinstan with a low Prandtl number, 0.03, is systematically investigated with/without the influence of the magnetic field. During the experiments, two thermostatic water baths are adopted to keep the upper copper plate and lower copper plate with constant temperature difference where the temperature of the upper copper plate is always lower than that of the lower copper plate. Thermoprobes are inserted in copper plates to record the temperature signal in the copper and liquid metal, while the ultrasonic sensors are inserted through the sidewall of the cell to measure the velocity distribution of liquid metal. From the velocity distribution in the cell, we observe three typical flow structures. Without the influence of the magnetic field, time-dependent large-scale convection is observed in the liquid metal thermal convection, with large velocity fluctuations near the cold and hot copper plates. The characteristics of velocity are similar to the thermal turbulence obtained from the normal liquid which is called as flow structure Ⅰ. Under the influence of the horizontal magnetic field, the thermal convection is strongly suppressed by the magnetic field, the stable single roll convection, namely the flow structure Ⅱ, and the double oscillation roll convection, namely the flow structure Ⅲ are observed. Furthermore, the characteristics of these two flow structures with the action of the horizontal magnetic field are investigated in detail through the velocity information obtained from three ultrasonic sensors.