Fluid Dynamic Problems in Cold Regions

1. 湍流的分离和再附着流是最基本的流之一，它与雪栅栏和遮蔽物的有效性有关，在雪漂移过程中阻碍驾驶员的视线等。对二维和三维分离流动进行了实验研究，得到了时间平均速度、湍流特性、大尺度旋涡结构脱落引起的流动不稳定性及其控制方法。这些结果很可能与大范围分离-再连接流的结果相似。采用实验方法研究了冷却空气和水沿同一方向流动时圆形管内分层冰水流动的冻结换热特性。实验在放水量、水温、管壁温度、放气量、水位等多种条件下进行。特别注意的是对正在形成的冰层的摄影视觉观察……更多的是沿着管壁。观察到冰的形成有两个不同的区域，一个是冻结区，另一个是稳态区。冻结开始的条件是根据经验公式得出的。在一定的雷诺数和冷却温度比范围内，在含有水的分支管道中形成冰生长。从流动可视化研究来看，支管流动的水首先被冰阻塞；随后分支部分下游的主管道被冻结，最终分支部分下游的主管道被冰阻塞。这表明，分支部分剩余水的冻结导致分支部分周围的管道破裂。用不同冷却温度比下的压力损失和雷诺数来表示成冰的瞬态行为。采用拟体坐标法，通过求解Navier-Stokes方程，对椭圆翼梯级组成的雪掩体的绕流进行了数值研究，得到了作用在翼上的气动力、速度分布和地面上的吹雪效果。在多孔板的尾迹处进行了速度和湍流测量，以评估板下游分离的低速区域的程度。这些结果为设计有效的雪栅栏和雪棚提供了很好的信息。少

1. A turbulent separated-and-reattaching flow is one of the most fundamental flows which are associated with the effectiveness of snow fences and shelters, the obstruction of drivers' sight during snow drifting, etc. Two- and three-dimensional separated flows were experimentally studied to obtain the time-mean velocities, turbulence properties, flow unsteadiness due to the shedding of large-scale vortical structure, and means of their manipulation. These results are likely to be similar to those of a wide range of separated-and-reattaching flows.2. An experimental study was made to investigate characteristics of the freezing heat transfer of layered ice-water flow in a circular pipe, in which cooled air and water flow in the same direction. The experiment was performed under a variety of conditions of water discharge, water temperature, tube-wall temperature, air discharge, and water level. Particular attention was focused on photographic visual observation of the developing ice layer … More along the tube wall. It was observed that there were two different regions characterizing the ice formation, one of which was the freeze-off region, and the other was the steady-state region. Conditions for the freezeoff onset were obtained in terms of an empirical formula.3. The formation of ice growth occurring in branched pipes which contained water was made over a range of Reynolds number, and the cooling temperature ratios. From the flow visualization studies, the branched pipe flowing water was first blocked by ice formation ; subsequently the main pipe downstream of the branched portion was frozen off, and eventually the main pipe downstream of the branched portion was blocked by ice formation. This shows that freezing of the remaining water in the branched portion results in the pipe rupture at around the branched portion. The transient behavior of the ice formation was expressed in terms of the pressure loss and Reynolds number for various cooling temperature ratios.4. Flow around a snow shelter consisting of cascade of elliptic wings was numerically studied by solving the Navier-Stokes equations by the use of a body-fitted coordinate to obtain the aerodynamic forces acting on the wing, the velocity distribution, and the effectiveness of blowing off snow on the ground level. Velocity and turbulence measurements were also made in wake of a porous plate to evaluate the extent of detached low-velocity region downstream of the plate. These results gave excellent information on design of effective snow fences and shelters. Less