SIMULTANEOUS MEASUREMENT OF TEMPERATURE AND VELOCITY BY STEREO LIQUID-CRYSTAL VISUALIZATION TECHNIQUE FOR STATISTICAL PROPERTIES AND COHERENT STRUCTURE OF TURBULENT RAYLEIGH-BERNARD CONVECTION

利用液晶测温技术和粒子图像测速技术对高Rayleigh数下湍流Rayleigh-Bernard对流中的温度和速度进行了同步测量。这些测量允许湍流的统计特性的评价和相干结构的知识相对于传热特性。除了测量平均流动和湍流特性外，还同时测量了温度脉动、湍流热流和耗散率。因此，湍流能量和温度波动的平衡评估从测量。结果表明，湍流能量的产生与对流层中的耗散率相平衡，并且随着靠近壁面而增加。另一方面，对流层中温度脉动的产生、耗散率、扩散和对流都很小，处于平衡状态，而在近壁处，由于温度梯度的存在，产生和耗散速率增大。三维同时测量温度和速度的扫描光片技术与热对流温度和速度的立体同时测量相结合。结果表明，对流层中的温度场和速度场具有相似的结构，表明速度场对羽流的发展有一定的影响。另一方面，羽流与壁面附近的轮辐结构之间的关系，通过液晶的温度和速度的同时多平面测量进行了检查。结果表明，辐状结构的生长导致了烟羽的形成和烟羽结构的发展。

The simultaneous measurements of temperature and velocity in a turbulent Rayleigh-Bernard convection at high Rayleigh number were carried out using the liquid crystal thermometry in combination with the particle image velocimetry. These measurements allow for the evaluation of statistical properties of turbulence and the knowledge of coherent structure with respect to the heat transfer characteristics. In addition to the measurement of mean flow and turbulence characteristics, the temperature fluctuation, turbulent heat flux and dissipation rate are measured simultaneously. Thus, the balances of turbulence energy and temperature fluctuation are evaluated from the measurements. It is found that the production of turbulence energy is balanced by the dissipation rate in the convection layer, and they increases as the wall is approached. On the other hand, the production of temperature fluctuation, the dissipation rate, the diffusion and the convection are all small and they are in balance in the convection layer, while the production and dissipation rate grows near the wall due to the presence of temperature gradient.The development of the plume structure is visualized by the three-dimensional simultaneous measurement of temperature and velocity by scanning light sheet technique in combination with the stereo simultaneous measurement of temperature and velocity in the thermal convection. It is found that the temperature contour and the velocity contour shows a similar structure in the convection layer, suggesting the influence of velocity field on the development of the plume. On the other hand, the relationship between the plume and the spoke structure near the wall was examined by the simultaneous multi-plane measurement of temperature and velocity by liquid crystals. The results show that the growth of the spoke structure leads to the formation of plume and the following development of plume structure.