Numerical investigation of dynamic stall of an oscillating aerofoil

The flow structure around an NACA 0012 aerofoil oscillating in pitch around the quarter-chord is numerically investigated by solving the two-dimensional compressible N-S equations using a special matrix-splitting scheme. This scheme is of second-order accuracy in time and space and is computationally more efficient than the conventional flux-splitting scheme. A 'rigid' C-grid with 149 x 51 points is used for the computation of unsteady flow. The freestream Mach number varies from 0.2 to 0.6 and the Reynolds number from 5000 to 20,000. The reduced frequency equals 0.25-0.5. The basic flow structure of dynamic stall is described and the Reynolds number effect on dynamic stall is briefly discussed. The influence of the compressibility on dynamic stall is analysed in detail. Numerical results show that there is a significant influence of the compressibility on the formation and convection of the dynamic stall vortex. There is a certain influence of the Reynolds number on the flow structure. The average convection velocity of the dynamic stall vortex is approximately 0.348 times the freestream velocity.

Free surface vibration in oscillatory convection of half floating zone

Projecting an orthographical grating mask (20pl/mm) on the surface of a small liquid bridge and receiving the reflected distortion image, one can calculate out reversely the shape of free surface of a liquid bridge. In this way we measured the surface shape of a small floating zone and the two-dimensional deformation of its vibration. The mechanism of thermocapillary oscillatory convection and the three-dimensional variation of the free surface are revealed experimentally. The principle for space experiment has been studied in our laboratory.

High-speed streams from coronal holes and the accelerating mechanism of the solar-wind

In this paper, the general Mach number equation is derived, and the influence of typical energy forms in the solar wind is analysed in detail. It shows that the accelerating process of the solar wind is influenced critically by the form of heating in the corona, and that the transonic mechanism is mainly the result of the adjustment of the variation of the crosssection of flowing tubes and the heat source term.The accelerating mechanism for both the high-speed stream from the coronal hole and the normal solar wind is similar. But, the temperature is low in the lower level of the coronal hole and more heat energy supply in the outside is required, hence the high speed of the solar wind; while the case with the ordinary coronal region is just the opposite, and the velocity of the solar wind is therefore lower. The accelerating process for various typical parameters is calculated, and it is found that the high-speed stream may reach 800 km/sec.

封闭和半封闭通风空间的环境流体问题

半封闭与全封闭空间的环境流体力学包括系统内的空气流动、温度和湿度分布以及污染物的凝积等问题，其中涉及控制空间的空气质量、通风设计以及预防水汽凝结等多个方面的研究．本文着重介绍国内外近年来相关的工作，研究如何从理论分析、实验研究以及数值模拟等方面入手，解决通风问题，以达到获得高通风效率、低能耗和提高空气舒适度的目的．研究的对象包括房间，建筑物，城市等半封闭空间，以及汽车、地铁、飞机、潜艇、载人航天飞行器等不同程度的全封闭空间．现有的理论研究已经从解释单点源纯浮力对流的基础模型发展到能够描述具有体积流量和动量流量的扩散流的湍流喷泉模型．然而，理论研究上的进步还不足以使它能够处理实际问题中多样的通风情况和复杂的空间结构，工程应用中还需更多依靠实验研究和数值模拟的结论．对载人航天飞行器中的环境流体问题的研究虽然刚刚起步，但其研究手段和经验可以从相对成熟的半封闭与全封闭空间的相关研究中获得借鉴．