水力机械叶片尾流机理研究

建立了基于弱可压缩流体基础之上的非恒定、粘性流数学模型,采用大涡模拟计算方法,固壁边界条件采用＂部分滑移条件＂,成功地对水力机械叶片尾流现象进行了模拟计算.计算结果表明,水力机械在非设计工况下,叶片绕流流态十分复杂,在负压面存在回流、脱流旋涡,以及叶片尾流.叶片正压面流速与叶片负压面流速差较大,加上负压面上的脱流旋涡,是形成叶片尾流的原因.尾流内存在周期性很好的类似卡门涡列的流动现象,其频率与叶片绕流状况有关,随着叶片入流角增加而增大,且属于低频范畴,因此,不能简单地采用圆柱绕流卡门涡街的频率公式进行计算.

Research on Mechanism of Trailing flow for Hydrofoils

The unsteady and viscous model based upon the weakly compressible flow has been established,Large Eddy Simulation(LES) approach is applied to simulating the mechanism of trailing flow of hydrofoils,and "partial-slip boundary condition " is developed for the solid wall boundary.The flow pattern around hydrofoil is very complex,containing back-flow,separation,vortex and trailing flow under the nonoptimum operation,the large velocity difference between the front and back surfaces at the exit of hydrofoil as well as the vortex on the back surface of hydrofoil cause the trailing flow,there is the periodically fluctuant pressure in the trailing flow,which is similar to Von Karman vortex street,and its frequency is increasing with the increase of hydrofoil's attacking angle,but it is the low frequency.So the frequency can't be simply calculated by the frequency formula of Von Karman vortex street around cylinder because Karman's formula is independent of hydrofoil's attacking angle.