低速轴流涡轮内部流动的大涡模拟

Large Eddy Simulations of Internal Flows Within a Low-Speed Axial Turbine

在低进口雷诺数下,低速轴流涡轮内部可能存在复杂的边界层转捩和分离流动。准确模拟边界层转捩和流动分离对低速轴流涡轮的气动设计具有重要意义。本文以某单级低速轴流涡轮为研究对象,采用大涡模拟方法对其在进口雷诺数为20000情况下的内部流动进行了数值模拟研究,并与前期采用全层流模型、S-A模型、Abu-Ghannam&Shaw(AGS)转捩模型的模拟结果进行了对比,对比分析发现,大涡模拟结果与实验结果吻合更好,可以准确模拟该涡轮叶片吸力面的流动分离和叶片通道内的二次流动。由大涡模拟结果可以得出,静叶尾迹和分离使尾迹区的流体流动速度降低,但尾迹对流动角的影响较小。动叶入口低速微团在做周向运动的同时沿径向运动;高速微团主要沿周向运动。静叶叶片表面的分离流存在较大的由叶顶向叶根的径向的运动;动叶吸力面叶顶处也存在较大的分离流动.

The internal flows within the low-speed axial turbine under low inlet Reynolds number is very complex, which usuMly includes boundary layer transition and flow separation. Accurate simulation of the boundary layer transition and flow separation are critical to aerodynamic design of the low-speed axial turbine. In this paper, large eddy simulation （LES） have been performed on the internal flows within a single stage low-speed axial turbine at inlet Reynolds number of 20000. The simulation results were compared with results of full laminar simulation, S^A model and Abu-Ghannam ＆： Shaw （AGS） transition model performed in previous studies. It was found by comparison with that the large eddy simulation result has better agreement with the experimental data, which captures more accurately the flow separation on the blade suction surface and the secondary flows within the blade passages. By analyzing the results of large eddy simulation, following conclusions are drawn. Both the wake and the separated flow of stator the lead to the reduction of the velocity in the wake zone. The wake flow has little impact on the flow angle turning. The low-velocity fluid at the inlet of the rotor moves in radial direction as well as circumferential direction; while, the high-speed fluid mainly moves in circumferential direction. The separation of the stator has obvious radial movement. Large flow separation has also observed at the tip of the rotor blade suction surface.