自调复合喷气叶顶密封抑制流体激振与减小流动损失机理研究

Fluid-induced vibration and flow loss in the tip seal have been the key issues and significant challenge for the safe and efficient operation of the turbomachinery. With the development of modern turbomachinery toward advanced parameters, it is still not clear about the method and mechanism of the fluid-induced vibration suppression and flow loss reduction. A new type of tip seal with self-regulated composite injection is proposed in this project. By employing multistage self-regulated nozzles in the sealing block and shroud ring, self-regulation of the flow structure in the tip seal is realized through making use of the natural pressure drop along the leakage path. Research on the mechanism of the fluid-induced vibration suppression and flow loss reduction is carried out as following: ① Based on the lumped parameter and perturbation method, the theoretical flow model in the tip clearance is setup to clarify its static and dynamic characteristics, as well as obtain the design method of the self-regulated nozzle. ② The flow field and the dynamic characteristics for the new seal is studied by numerical calculation and dynamic pressure measurement, as well as the unbalance synchronous excitation method in the frequency domain. Then the mechanism of the fluid-induced vibration suppression is revealed. ③ The multi-zone model including the main flow cascade and the tip seal is presented. The pressure distribution in the inlet, interior and outlet of the tip seal gap is measured to analyze the characteristic of turbulent dissipation, shaft work, mixing loss and angle attack loss. The mechanism of flow loss reduction is further illuminated. The project puts forward a new type of tip seal and reveals the mechanism of the fluid-induced vibration suppression and flow loss reduction, as well as provides a new way to improve the tip seal stability and flow efficiency.

叶顶密封流体激振及间隙流动损失是透平机械安全与高效运行的关键问题与重要挑战。然而随着机组向高参数发展，抑制流体激振及减小流动损失的方法与机理尚不明确。本项目提出新型自调复合喷气叶顶密封，通过在密封块与围带上引入多级自调喷嘴，并利用流体沿泄漏路径形成的自然压差，实现流动结构的自调控；开展新型密封抑制流体激振与减小流动损失机理研究：①基于集中参数与摄动方法建立叶顶间隙流体流动理论模型，探明其动静特性及自调喷嘴设计方法；②应用数值计算、动压测试及基于不平衡同频激励的频域实验方法研究密封流场与动力特性，揭示新型密封抑制流体激振机理；③建立包含通流叶栅与叶顶密封的多域流场分析模型，实验测试密封间隙及进出口压力分布，研究湍流耗散、轮周功、掺混损失及攻角损失特性，阐明新型密封减小流动损失机理。本项目提出一种新型叶顶密封结构，揭示其抑制流体激振与减小流动损失机理，为提高叶顶密封抗失稳与增效能力提供新方法。

密封流体激振及间隙流动损失已成为高参数透平机械发展的瓶颈与关键问题，本项目提出新型自调复合喷气叶顶密封，以期达到抑制叶顶密封引起的流体激振、减小泄漏流体导致流动损失的目的。. 项目首先开展了环形密封动静特性基础理论研究：研究了环形密封阻塞/非阻塞工况下静态稳定性及动力学特性；基于热力学理论研究非均匀间隙密封临界压比计算方法，可有效判别非均匀间隙密封临界状态；计算分析了预旋对迷宫密封动静特性影响，提出迷宫密封“穿越齿数”与“临界稳定性”概念，阐明了进口预旋的作用机制，并给出了进口预旋方向选取准则；给出了梳齿密封阻旋栅有效性的定量分析与判别标准。. 其次，开展了自调喷气式迷宫密封抑制流体激振与减小流动损失机理、影响因素及结构优化研究：以单个密封腔为单元对密封气流激振机理开展研究，开展自调喷嘴结构优化设计，分析喷气形式/角/数量等因素对密封动力特性系数、周向速度/压力等参数的影响；提出新型自调逆滞流迷宫密封结构，通过在密封齿上设计微型逆滞喷管，连通相邻密封腔，利用相邻腔室压差产生逆向射流，对密封腔内周向流动进行自调节，相较于贯通式逆滞流迷宫密封，间隔式逆滞流迷宫密封在各涡动频率下表现出更高的稳定性，特别在高涡动频率下，间隔式逆滞流密封有效阻尼系数为传统迷宫密封的200%，逆滞喷管的增加大幅提高了原结构迷宫密封的稳定性。. 最后，开展了密封动力特性系数数值识别方法及密封动静特性实验研究：提出了基于微元理论的密封动力特性系数识别方法、基于加速扫频与涡动轨迹分解的密封动力特性系数识别方法；设计搭建了密封动力特性实验识别实验装置，开展了基于阻抗法的密封动力特性系数实验识别。. 研究成果将为推动航空发动机、燃气轮机、压缩机及汽轮机等透平机械密封设计理论及其高参数化提供理论基础和实现途径。