高负荷低压涡轮轮毂端区复杂流场的演化机理及其调控技术研究

Low pressure turbine (LPT) is a key component of modern aeroengines. Generally, there are many stages in the LPT, which means that the LPT is heavy. The efficiency of the LPT strongly influences the performance of the engine. Advanced LPT tends to decrease blade count in order to reduce weight, production cost and improve reliability of the turbine. Unfortunately, low blade count results in an increased aerodynamic airfoil load. High loading and low Reynolds number condition make the aerodynamic losses of the LPT rise, and the effect of endwall flows is increasingly significant. Reducing endwall secondary flow losses has become the key point for the successful design of highly-loaded LPT. To effectively organize and control endwall flow field, it is necessary to further understand the spatio-temporal evolution mechanism of the complex endwall flows. In this project, through the improvement of the large-eddy simulation (LES) code, detailed calculations of the LPT endwall flow field under different conditions are conducted and the LES databases are constructed. By exploring the evolution and interaction mechanism of the complex secondary vortices, and the evolution of endwall and blade boundary layer, the loss generation mechanism of the endwall region are revealed. And the correlations of aerodynamic losses and endwall complex flow fields are also discovered. On this basis, the existing endwall region flow organization and control techniques are improved to further reduce the aerodynamic losses. The improvement will finally apply to the design of the future LPT components.

低压涡轮是现代航空燃气轮机的重要组成部件，级数多、重量大，其效率显著影响发动机整机性能；为降低重量和制造成本、提高部件可靠性，先进低压涡轮趋于减少叶片数，由此导致叶片负荷明显增加。高负荷和较低的工作雷诺数使得低压涡轮气动损失上升、且端壁效应在其中的影响日益显著，降低端区损失已成为决定高负荷低压涡轮设计成败的关键；而要有效的组织和控制端区流场，就必须进一步深入认识高负荷条件下端区复杂流动的时空演化机制。本项目通过完善大涡模拟程序，对不同流动条件下的低压涡轮轮毂端区流动进行细致模拟，建立数值数据库。通过探讨端区复杂涡系结构的相互作用机制和发展演化机理、端壁/叶型表面边界层的流态演化过程，研究端区气动损失的产生机制，揭示气动损失与端区复杂流动图画的关联关系。在此基础上尝试改进现有的端区流动组织和控制技术，进一步降低端区气动损失，为未来高负荷高性能低压涡轮部件的设计服务。

低压涡轮是现代航空燃气轮机的重要组成部件，级数多、重量大，其效率显著影响发动机整机性能；为降低重量和制造成本、提高部件可靠性，先进低压涡轮趋于减少叶片数，由此导致叶片负荷明显增加。高负荷和较低的工作雷诺数使得低压涡轮气动损失上升、且端壁效应在其中的影响日益显著，降低端区损失已成为决定高负荷低压涡轮设计成败的关键；而要有效的组织和控制端区流场，就必须进一步深入认识高负荷条件下端区复杂流动的时空演化机制。本项目以大涡模拟为主要研究手段，结合雷诺平均方法，通过分析真实运行环境中高负荷低压涡轮轮毂端区流动的特征，建立数值仿真模型；在此基础上挑选典型工况进行计算，获得了不同流动条件下的轮毂端区流场。研究发现：无论对于大涡模拟或者雷诺平均方法，来流端壁边界层的设定均是关系仿真成败的关键，通常需要通过独立的计算给定；而端壁边界层的状态对端区二次流动图画也具有第一位的影响，湍流边界层带来远大于层流边界层的气动损失；轮缘间隙及封严冷气的存在会对上游来流边界层造成显著影响，在机理研究中是不能被忽视的重要因素。本项目的研究成果可用于改进现有的端区流动组织和控制技术，进一步降低端区气动损失，也为未来进一步的机理研究指出了一个可能的方向。