Development of New Ultrasonic Measurement System for Turbulence and Elucidation of the Limit of Transport in Turbulence

湍流的研究在各个科学技术领域都具有重要意义。其中热湍流一直是热门的研究课题，因为热湍流中的热输运、扩散和混合预测是基础研究和应用研究必不可少的。本课题旨在建立一种新的热湍流超声测量方法，并对湍流内部的结构进行研究，以阐明湍流引起的热输运的标度规律。我们用水银作为测试液体。由于其运动粘度低，动力边界层比热边界层薄，使我们能够在实验室中探索高瑞利，高雷诺数。虽然超声波测速仪（USV）用于流速测量已经很长时间了，但由于时间分辨率和可获得的最大速度的限制，它从未被应用于湍流的测量。更重要的是，即使在瑞利数高的情况下，热湍流的最大速度和最高频率也比网格湍流和尾迹湍流等其他湍流要低。我们开发了三种热湍流测量系统。三个超声波换能器沿X、Y、Z轴同时监测。2. 一个移动的换能器，而不破坏对流电池的壁。3. 多个热敏传感器（32个热敏电阻）嵌入电池底部和侧壁，使我们能够监测热湍流中平均流量的结构。利用这些测量系统，我们成功地从速度场的瞬时测量中直接测量了能谱，而不使用Taylor假设，并发现Bolgiano-Obkhov标度定律在热湍流中成立。进一步阐明了热湍流中存在的平均流的结构。它们的结构、动力学和稳定性在很大程度上取决于对流电池的宽高比。少

Study on turbulence is important for every area of science and technology. Among them thermal turbulence has been popular research subjects, since the prediction of heat transport, diffusion and mixing in thermal turbulence is indispensable fur both fundamental and application researches. In this research project we aimed to develop a new ultrasonic measurement method far thermal turbulence and explore stricture in turbulence to elucidate the scaling law of beat transport due to turbulence. We used mercury as a test liquid. Because, the fact that its kinematic viscosity is low and kinetic boundary layer is thinner than the thermal boundary layer enables us to explore high Rayleigh, high Reynolds number in laboratory Although ultrasonic velocimeter (USV) is known for long time for flow rate measurements, it has never been applied to measurement of turbulence due to limitation in temporal resolution and accessible maximum velocity We succeeded to use USV for thermal turbulence, because t … More he maximum velocity and the highest frequency in thermal turbulence is relatively low even at high Rayleigh number compared with other turbulence, such as grid turbulence and wake turbulence. We developed 3 measurement systems far thermal turbulence 1. Three ultrasonic transducers monitoring along X, Y, and Z axes simultaneously. 2. One moving transducer without destructing the wall of the convection cell. 3. Multi-thermosensors (32 thermistors) embedded in the cell bottom and the side wall which enable us to monitor the structure of the mean flow in thermal turbulence. By using these measurement systems, we successfully measured the energy spectrum directly from instantaneous measurement of the velocity filed without utilizing Taylor hypothesis, and found that Bolgiano-Obkhov scaling law holds in thermal turbulence. We further elucidated structure of the mean flow existing in thermal turbulence. Their structures, dynamics, and stabilities strongly depend on the aspect ratio of the convection cell. Less