沟槽面在湍流减阻中的应用

APPLICATION OF MICRO-GROOVED SURFACE FOR TURBULENT DRAG REDUCTION

对近些年来的沟槽面湍流减阻技术的工业应用方向 ,沟槽的几何形状和尺度、流场压力梯度、沟槽面放置方式对于沟槽减阻效能的影响 ,沟槽面对于湍流边界层流动特性的影响 ,沟槽面的湍流减阻机理几方面研究进展进行了综述。从湍流拟序结构理论出发提出 :具有减阻效应的沟槽面不但能通过控制低速制条带间距来降低湍流“猝发”频率 ,而且在“猝发”后的高速“下扫”过程中因其几何结构使藏在槽内的安静流体避免或部分避免因高速“下扫”而“诱导”出较大速度剪切层 ,从而实现减阻。同时指出需要利用先进的实验技术如PIV等图像处理手段并结合直接数值模拟对湍流边界层的瞬时流场进行研究 ,以其找出湍流边界层的流动结构及其运动规律。

The recent developments of investigations on the applications of drag reducing micro-grooved surface to industry, the influence of groove's shape and size, pressure gradients in flow field, the surface installation means on drag reduction effect, the changes of turbulent boundary layer's characteristics caused by this surface and the drag reduction mechanism were summarized bere. On the basis of the coherent structure theory, It was proposed that the drag reducing grooved surface can not only control the spaces between two low-speed streaks to further reduce turbulent burst frequency, but also make a part or the whole quiet fluid in grooves avoid encountering the high-speed fluid from the upper layer downwash and a higher shear stress induced by it. Thus, turbulent drag reduction can be achieved. It was also suggested that the means of certain advanced technology such as PIV image processing method combined with the direct numerical simulation should be used in the research of instantaneous flow field in turbulent boundary layer over grooved surface in order to find out the drag reduction methanism.