Experimental Study on the Transition to Superfluid Turbulent Flow

尝试了几种实验方法来研究超流体向超流体管状流的转变，得到了以下结果：i)应用流动显示技术和激光多普勒测速仪对热逆流射流进行了测量：特别是研究了热激发的第二声亥姆霍兹振荡，以揭示振荡现象出现的条件，并分析了由于向超流体湍流转变而对振荡的调制。实验结果与线性稳定性分析的预测结果相吻合。这一事实似乎表明，对于小扰动和慢扰动情况，Gorter-Mellink互摩擦项是一个令人满意的近似。ii)双流体方程的数值模拟(热激波分析)：引入Gorter-Mellink项和涡旋密度方程evol…的影响比较了两种描述纠缠涡与激波相互作用的唯象描述的控制方程，以了解相互摩擦引起的波形变化。比较表明，后一种处理方法提供了更好的结果，但这两种方法仍然不足以定量估计。iii)超流体湍流(非线性)区域内喷泉效应泵元件的流动测量：指出在描述流动现象时应考虑元件的内部结构。在考虑内部结构的流动模型的基础上，编制了计算程序来预测泵的性能和最大流量。iv)激光全息干涉法在超流体测量中的应用：包括带光学窗口的低温恒温器的实验装置的搭建接近完成，并成功地进行了初步实验。为了研究强热激波后纠缠涡旋的产生以及He II场向超流湍流态的转变，即将启动He II中的热激波实验。研制了一种用于热冲击波探测的金锡超导薄膜温度探测器。较少

Several experimental approaches are attempted for the study of the transition of superfluid flow to superfluid tubulent flow, and the following results are obtained.i) Measurement of the thermal counterflow jet by applying a flow visualization tecnique and with a laser Doppler velocimeter : In particular, thermally excited 2nd sound Helmholtz oscillation is investigated to elusidate the condition for the appearance of the oscillation phenomena and to analyze the modulation to the oscillation as a result of the transition to the superfluid turbulent flow. The experimental results are found to agree with the prediction by the linear stability analysis. This fact seems to indicate that the Gorter-Mellink mutual friction term is a satisfactory approximation for the cases of small and slow disturbances.ii) Numerical simulation for the two-fluid equations (analysis of a thermal shock wave) : The effects of the introduction of the Gorter-Mellink term and of the equation of vortex density evol … More ution to the governing equations, both of which are phenomenological description for the interaction of the tangled vortices with a shock wave, are compared to see the wave form modification caused by the mutual friction. The comparison suggests that the latter treatment provides far better result but both approaches are still insufficient for a quantitative estimation.iii) Measurement of the flow through a fountain effect pump element in the superfluid turbulent flow (non-linear) region : It is indicated that the interior structure of an element should be taken into account to describe flow phenomena. A computer program on the basis of the flow model taking account of the interior structure is completed to predict the pump performance and the maximum flow rate.iv) Application of the laser hologram interferometry to superfluid measurement : The construction of the experimental apparatus including a cryostat with optical windows is nearly completed, and a preliminary experiment is successfully made. Experiment of a thermal shock wave in He II will be soon started to study the generation of tangled vortices behind a strong thermal shock wave and thus the transition of the He II field to the superfluid turbulent state. An Au-Sn superconducting thin film temperature detector for the thermal shock wave detection is manufactured and tested. Less