ABSTRACT

The present study aims at the investigation of the transition of the natural convective flow in a water-filled differentially heated cubic enclosure. The schlieren-particle image velocimetry (PIV) system has been developed and employed for simultaneous measurement of ray-averaged velocity and temperature fields from transient schlieren images for distinct Rayleigh number (Ra) (1 × 10⁷ ≤ Ra ≤ 5 × 10⁸). The experimentally obtained results have been compared with three-dimensional computational results. The three-dimensional incompressible simulations are carried out for a wide range of Ra (1 × 10⁵ ≤ Ra ≤ 5 × 10⁸), treating the density difference using Boussinesq approximation. The results from present simulations show that the flow is found steady in the range of Ra (1 × 10⁵ ≤ Ra ≤ 1 × 10⁸) while the critical Ra, at which the steady flow becomes unsteady, lies between 1 × 10⁸ and 5 × 10⁸. The critical Ra from the experiments is found to lie between 4 × 10⁸ and 5 × 10⁸. Also, the three-dimensionality effect on large-scale temperature field is found to decrease as Ra increases.

摘要

本研究旨在研究充满水的差热立方体外壳中自然对流的转变。纹影粒子图像测速 (PIV) 系统已开发并用于同时测量瞬态纹影图像的射线平均速度和温度场，用于不同的瑞利数 (Ra) (1 × 10 7 ≤ Ra ≤ 5 ^× 10 ⁸ ) . 将实验获得的结果与三维计算结果进行了比较。三维不可压缩模拟在很宽的 Ra 范围内进行 (1 × 10 ⁵ ≤ Ra ≤ 5 × 10 ⁸), 使用 Boussinesq 近似处理密度差异。^{目前的模拟结果表明，在 Ra (1 × 10 5} ≤ Ra ≤ 1 × 10 ⁸ )范围内流动稳定，而稳定流动变得不稳定的临界 Ra 介于 1 × 10 ⁸和5 × 10 ⁸。发现实验中的临界 Ra 介于 4 × 10 ⁸和 5 × 10 ⁸之间。此外，还发现随着 Ra 的增加，对大尺度温度场的三维效应降低。