Simultaneous volumetric measurement of the velocity and temperature field in Rayleigh-Bénard cells with large aspect ratio

该项目的主要目标是确定湍流超结构对大宽高比瑞利-伯纳德流动中热量和动量传递的影响，即与高度相比的大横向尺寸(Γ=25、20和10)。对于这些大的高宽比，湍流上层建筑的典型侧向尺寸是高度的2到3倍。时间演化非常缓慢，这就需要进行长时间的观测。为此，我们将用瑞利数在5×105~108范围内的光学测量技术，对带有透明冷却板的充水Rayleigh-Bénard槽中的流动进行实验研究。为了在水平面内同时测量速度和温度，热致变色液晶(TLC)将作为示踪粒子用于立体粒子图像测速和体积粒子跟踪测速。温度将根据TLC的颜色外观确定。目前实验的主要好处是它在非常长的时间跨度(长达几天)内的稳定性，这使得能够进行具有高空间分辨率和高统计相关性的长期测量。由于目前只能进行短期的数值模拟，因此可以首次研究湍流超结构的长期演变。该项目是优先方案内其他项目的数据提供者，并受益于开发其他项目的数据分析技术。

The main objective of the project is to determine the influence of the turbulent superstructures on the heat and momentum transfer in Rayleigh-Bénard flows with large aspect ratios, i.e. large lateral dimensions in comparison to height (Γ = 25, 20 and 10). For these large aspect ratios the typical lateral dimensions of the turbulent superstructures are 2 to 3 times the height. The temporal evolution is very slow, which makes long-time observations necessary. For this reason the flow in a water filled Rayleigh-Bénard cell with transparent cooling plate will be experimentally investigated with optical measurement techniques for Rayleigh numbers in the range of 5×105 to 108. To simultaneously measure velocity and temperature in the horizontal plane, thermochromic liquid crystals (TLCs) will be used as tracer particles for stereoscopic particle image velocimetry and volumetric particle tracking velocimetry. The temperature will be determined based in the color appearance of the TLCs. The main benefit of the current experiment is its stability over very long time spans (up to days) which allows for long-time measurements with high spatial resolution and high statistical relevance. Since so far only short time numerical simulations are available the long term evolution of the turbulent superstructures can be investigated for the first time. The project serves as data provider for other projects within the priority programme and benefits from the development of data analysis techniques from other projects.