Effects of vortical structures in a multi-phase flow on the thermal and mass transfer

在1999年和2000年，我们花了大量的时间来研制实验设备和编写新的仿真代码。首席调查员编写了一个非常准确的Fortran代码来模拟封闭域内的流动。他精心布置网格点进行高分辨率模拟，得到了最优的网格布置。还需要将速度场、压力场和温度场错开排列，以防止人为数值不稳定的发生。另一位研究者建造了一个方形截面的长管道来测量带有非常小气泡的湍流。他通过振荡一侧壁面注入气泡，用LDV测量速度场。2001年，首席研究员通过可视化AVS检查了立方体中的自然对流。研究发现，随着时间的推移，流型发生变化，最终达到一个涡流。对非线性项采用保守或非保守形式进行数值计算的适宜性进行了研究。在最后一年，2002年，首席研究员研究了立方体自然对流中小颗粒的扩散，瑞利数从5000到12000不等。他发现了先前在空腔流中发现的流线混沌的存在。结果表明，环面中存在两个环面和两条固定线。非常有趣的是，在空腔流的流线混沌中，混沌结构随雷诺数的增加变化很大，而在自然对流中，混沌结构随瑞利数的增加变化不大。

In 1999 and 2000, we spent research time for creating experimental apparatus and making new simulation codes. Head investigator coded a very accurate Fortran code to simulate flows within a closed domain. He carefully arranged the mesh points for high resolution simulation and obtained optimal mesh arrangement. It is also necessary to arrange velocity, pressure and temperature fields in a staggered way to prevent artificial numerical instability to occur. Another investigator constructed a long duct with a square cross section to measure turbulent flow with very small air bubbles. He injected air bubbles by oscillating one side wall and measured velocity field by LDV. In 2001, the head investigator examined a natural convection in a cube by visualizing AVS. It is found that the flow pattern changes as time proceeds and finally attains one vortex flow. It is also studied on the appropriateness of numerical calculation by conservative or non-conservative form for the nonlinear terms. In the final year, 2002, the head investigator studied diffusion of small particles in a natural convection in a cube over the Rayleigh number from 5000 up to 12000. He found an existence of the stream line chaos as found in a cavity flow before. It is found that there exist two tori and two fixed lines within them. It is very interesting that though in stream line chaos of the cavity flow, the structure of chaos varies largely as the Reynolds number increases, in the case of the natural convection, the structure of chaos varies little as the Rayleigh number increases.