轮盘结构对向心涡轮内部流动影响的数值研究

Numerical Study for Effects of Scalloping on Performance of Radial Turbine

关键词:  向心涡轮  轮盘轻量化  叶背间隙流  盘腔冷气  数值模拟

Key words:  Radial turbine  Wheel lightening  Backface clearance flow  Cooling air  Numerical simulation

摘要:

采用数值方法对燃气轮机带有冷气封严的向心涡轮开展研究，对比分析了不同轮盘结构向心涡轮总体气动参数差异及内部复杂二次流的动力学机制。研究表明：扇形与深度扇形向心涡轮相比常规结构效率分别下降1.7%，3.5%，冷气量分别降低12.2%，16.3%，冷气量主要由高速旋转盘的“泵吸效应”决定。叶背间隙泄漏流在进入流道处受同向的离心力及科氏力，表现为向叶顶方向运动；盘腔冷气在进入流道处受到的离心力与科氏力相反，且科氏力占主导地位，表现为贴壁运动；在往下游运动过程中两股流体逐渐演变为主要受离心力影响并向叶顶发展。深度扇形向心涡轮冷气与叶背泄漏流掺混后，在流道中部形成大尺度旋涡，是其气动效率显著下降的根本原因。

Abstract:

The numerical simulation method is used to study the radial turbine of a gas turbine with the cooling air seal. The overall aerodynamic parameters of the different scalloped radial turbines and the dynamics mechanism of internal complex secondary flow are analyzed in detail. The research shows that the efficiency of scalloped and deeply scalloped radial turbines decreases by 1.7% and 3.5%, and the mass flow of cooling air decreases by 12.2% and 16.3% compared with unscalloped radial turbine. The mass flow of cooling air is mainly determined by the ‘pump effect’ of the high-speed rotating disk. The backface leakage flow is subjected to centrifugal force and Coriolis force in the same direction at the entrance to the passage, which moves forward the tip. However, the centrifugal force of the cooling air is opposite to the Coriolis force at the entrance to the passage and the Coriolis force is the dominant force, which makes the cooling air move along the wall of hub and blade. After mixing with the main stream, the above two fluids are mainly subjected to centrifugal force and moves to the tip. In the deeply scalloped radial turbine, the cooling air and backface clearance flow are mixed to form a large-scale vortex at the middle of the passage, which is the main reason for the significant efficiency decline.