高负荷低展弦比氦涡轮端壁损失机理研究

以某多级氦涡轮第一级为研究对象，借助数值模拟技术对低展弦比涡轮动静叶端壁通道涡迁移及干涉机制进行研究，并考察了叶片弯曲对涡轮气动性能的影响。结果表明：受下端壁道涡影响，导叶出口近叶根处气流过偏转，导致转子前缘近轮毂区正攻角变大；叶片根部负荷增加，致使马蹄涡压力面分支与吸力面分支交点前移；下端壁通道涡径向迁移至近叶顶区，其与叶尖泄漏涡相互影响致使叶顶区粘性损失显著增加。弯叶片对低展弦比大折转涡轮叶片的作用效果与传统涡轮具有明显差别：叶片正弯时叶顶载荷减小，导致叶顶间隙泄漏涡与通道涡强度及损失显著减小，涡轮性能得到改善；叶片反弯时叶顶载荷增加，致使叶尖泄漏损失增大，且强径向压力梯度作用下下端壁低能流体向叶顶汇聚，损失显著增加。

Investigation on Endwall Loss Mechanism of a Highly Loaded Helium Turbine with Low Aspect Ratio

The development of passage vortices in a low aspect ratio helium turbine is numerically analyzed. The influence of bow blades on the aerodynamic performance of the turbine is also studied in this paper. Under the influence of the hub passage vortex, exit flow angles close to stator roots increases. It results in the increasing of incidence angles at rotor leading edge. The cross-channel pressure gradient at that region is raised, and then the meeting point of the passage vortex moves close to the rotor leading edge. The hub passage vortex migrates to the blade tip region. The low momentum fluid from the hub region moves along with the hub passage vortex and mixes with the tip leakage flow, which causes significant flow losses at the tip region. To optimize the turbine performance, bow blade is utilized to reduce the endwall viscosity losses. The positive bow rotor reduces the rotor tip loading. The intensity of the tip leakage vortex and passage vortex are decreased, and the turbine performance is improved. The negative bow rotor enlarges the rotor tip loading, which increase the intensity of the tip leakage flow. The low momentum fluid from the hub region is also move to the blade tip, which caused by larger radial pressure gradient compared with the one of the positive bow blade. The flow losses thus increase and the turbine efficiency deteriorates.