涡轮叶栅非轴对称叶冠组织端区高效流动的机理研究

The introduction of the blade shroud induces complex flow phenomena in the shroud cavity, which still has great impact on turbine aerodynamics, and increases the shroud weight at the highest radius leading to increased stresses which rapidly approach the structural limits of the blades. With the purpose of reducing the shroud weight, the partial shroud intensifies the interaction between shroud cavity flows and main flows, and then deteriorates turbine endwall flow field and efficiency. Therefore, based on the integrated blade-shroud design philosophy, the scientific issue about the relationship between shrouded tip endwall flow interaction mechanisms and the shroud structure parameters is proposed, and then the corresponding investigations are performed. Besides, in order to verify the concept both of the organization of the shrouded tip endwall flow and of the reduction of the shroud weight by optimizing the nonaxisymmetric shroud structure, the combination of the shroud cavity flow experiment, unsteady numerical simulation as well as blade-shroud coupling method, and theoretical analysis is used to study the mixing processes of shroud cavity flows and main flows, the coupling relationship between the shroud structure parameters and the endwall unsteady flow characteristics, and aerodynamic loss mechanisms. Through the study, the project intends to reveal the interaction mechanisms between shroud cavity wall shear flows, leakage jet flows and vortex flows inside the narrow space at the inlet and exit of the shroud cavity, and its relationship with the shroud structure parameters, to establish an aerodynamic loss model associated with different shroud structures, and then to explore the design principles of the optimum nonaxisymmetric shroud structure that can effectively reduce the endwall flow losses. The research results can provide the theoretical basis and the technical support for the optimum design of a new shroud structure and the control of endwall aerodynamic losses, and then promote the development of the integrated blade-shroud design technology.

涡轮叶片带冠形成了叶冠容腔内及进出口特有的泄漏流现象，使得容腔结构和泄漏流仍对涡轮性能有很大影响；同时，带冠增大了叶片应力，而旨在减少叶冠质量的部分叶冠又加剧了叶冠容腔流与主流的掺混，严重影响涡轮效率。为此，本项目提炼出叶冠端区流动干涉机制与其结构参数的内在关联这一科学问题并展开研究，通过叶冠容腔流试验、叶片-冠耦合数值模拟结合理论分析等手段，对叶冠泄漏流与主流的掺混过程及流场特性、叶冠几何参数与非定常流特性的耦合关系和气动损失机理进行研究，验证申请人提出的采用并优化非轴对称叶冠形式以重组叶冠端区流动并实现叶冠减重的构想。通过研究，揭示狭小空间内壁面剪切流、射流与涡流的掺混机制与结构参数的关联，建立适应不同叶冠结构的气动损失模型，进而探求能有效降低端区损失的最佳非轴对称叶冠设计准则。研究结果能为新型叶冠结构研发和端区气动损失控制提供理论依据和技术支撑，促进涡轮叶片-冠一体化设计技术的发展。

涡轮叶片带冠形成了叶冠容腔内及进出口特有的泄漏流现象，使得容腔结构和泄漏流仍对涡轮性能有很大影响；同时，带冠增大了叶片应力，而旨在减少叶冠质量的部分叶冠又加剧了叶冠容腔流与主流的掺混，严重影响涡轮效率。为此，本项目提炼出叶冠端区流动干涉机制与其结构参数的内在关联这一科学问题并展开研究，通过叶冠容腔流试验、叶片-冠耦合数值模拟结合理论分析等手段，对叶冠泄漏流与主流的掺混过程及流场特性、叶冠几何参数与非定常流特性的耦合关系和气动损失机理进行研究，验证申请人提出的采用并优化非轴对称叶冠形式以重组叶冠端区流动并实现叶冠减重的构想。.首先，深入研究了涡轮叶冠端区流场及损失特点，在此基础上基于对带冠和不带冠涡轮叶顶间隙端区二次流动干涉机理的对比研究，着重探讨了带冠涡轮间隙端区上游尾迹、泄漏涡/掺混区和下游机匣通道涡之间的相互干涉机理。其次，通过建立若干不同的部分叶冠结构和非轴对称优化叶冠结构，展开了叶冠容腔流试验和流热固耦合计算研究，结果指出：提出的非轴对称叶冠结构在降低叶片总应力的基础上可有效组织和控制叶冠容腔泄漏流和通道主流的相互作用和掺混，改善涡轮端区性能。再次，研究了自发射流技术应用于涡轮叶冠端区精细流动组织的机理，结果表明：在带冠叶片压力面上部的叶冠上下表面之间贯穿开孔的自发射流设计能进一步优化叶冠内部流动，带冠叶片总压损失总体上约降低2.4%。最后，结合试验与数值计算结果，通过理论分析的方法构造了适应不同叶冠结构的端区泄漏损失预测模型，预测精度满足工程需求。.本项目的研究成果为涡轮新型叶冠结构研发和端区气动损失控制提供了理论依据和技术支撑，促进了涡轮叶片-叶冠一体化优化设计技术的发展。