水力机械三维分离准则的探讨

水力机械的分离为三维流动，三维流动的侧向压力梯度产生边界层的二次流动。文中将边界层内的速度分布分为近壁粘性层和接近于主流的外层两部分，通过研究垂直于主流方向的二次流动和主流的相关性，结合三维分离线的邻近流动特性分析提出了通过主流流场参数和沿流向的二维边界层流动来判断三维流动分离的准则。在垂直于三维分离线的截面内，其流动性态和二维分离相类似。边界层的二次流动和侧向压力梯度，以及二者的相互作用是影响水力机械三维流动分离的重要因素。当主流逆压梯度的方向与二次流动的方向均在主流方向一侧时，流动的三维效应使得三维流动比二维流动不容易分离。当主流逆压梯度的方向与二次流动的方向分别在主流方向的两侧时，三维流动较易产生分离

Discussions about three dimensional criterion of flow separation in hydraulic machine

The separation flow is three dimensional in hydraulic machine.The pressure gradient in cross direction produces secondary flow in boundary layer.The velocity distribution in boundary layer is devided into the inner viscous layer and the outer layer.By correlating the main flow and the secondary flow normal to the main flow,and studying the flow characteristic near the three dimensional separation line,a criterion to predict three dimensional flow separation has been given out.In the section normal to the three dimensional separation line,the flow characteristic is simliar to that of the two dimensional flow separation .The different angle between the directions of the secondary flow and the adverse gradient has different effect on the flow separation .The flow point which is far from the two dimensional separation point may be separation point in three dimensional flow.The point which is near the two dimensional separation point is also near the three dimensional separation point.The correlation factor A between the main flow and the secondary flow has great effect on the relative location of the three dimensional flow separation point.