自适应气膜复合密封抑制透平叶尖泄漏理论、关键技术与可行性研究

The project presents a new kind of turbine blade tipclearance seal theory with self-adaptive ability to reduce clearance leakage and enhance seal reliability. Gas film seal was introduced into the gap between the cylinder chamber and the traditional shround labyrinth seal. The gas film squeezing effect, the tip throttling effect and the cavity dissipation effect were combined together. Clearance self-adaption ability was realized by the specially designed sealing ring with high flexibility and gas film with large stiffness.The three dimensional CFD model including disk-blade-seal system will be set up to calculate seal leakage ratio, gas film thichness and dynamic characteristics. Influence of end face interface characteristic, structural parameter and operation condition on gas film and seal performance will be researched. The simplified model based on the Reynolds equation of gas film seal and the two-bulk-flow model of the labyrinth seal will be presented to simulate the follow-up and the stability performance of the seal during rup up and run down process of the unit under large variable condition operation and large external disturbance. Key technology of the new kind of seal, such as clearance self adaptive ability, reliability and follow up ability will be deeply researched. Test of leakage, wear resistance and reliability will be done on seal rig. The impedance test and the impulse test are put forward to measure seal dynamic characteristics and follow up performance. The performance of the new kind of seal will be evaluated objectively and comprehensively on the base of the above mentioned theoretical and experimental research.

为了减小透平叶尖泄漏，提高密封可靠性，提出新型自适应动压气膜复合叶尖密封理论。在气缸腔室与梳齿密封之间引入端面气膜，将气膜挤压、齿间节流和腔内耗散等效应复合在一起。通过高柔性密封环和大刚度气膜设计实现密封间隙的自适应调整。考虑气膜、节流、膨胀耗散等效应，建立叶轮—叶片—密封整体三维CFD模型，求解泄漏量、膜厚、气膜动力特性等，分析密封界面特性、结构参数、工况条件等对气膜和密封性能的影响。基于Reynolds方程和双控制体方法，建立复合密封简化模型，分析密封环在启停机等大幅变工况和扰动下的随动性能和稳定性。对复合密封若干关键技术，如：间隙自适应能力、可靠性、随动性等进行深入研究。构建气膜复合密封定量设计分析准则。在密封试验台上研究新型密封泄漏特性、耐磨性和可靠性，通过阻抗和冲击试验等测试密封动力特性和随动性能。在上述理论和试验研究基础上，全面客观地地评价新型动压气膜叶尖复合密封的性能

本项目首先研究了自适应气膜密封控制模型。气膜密封内流体流动可以归为进出口压差使流体在半径方向上的泊肃叶流和动静环表面相对速度使流体在圆周方向上的库特流。气膜密封泄漏抑制能力优于梳齿密封，流体力指向轴向，不存在激振问题。Whipple理论低估了气膜密封承载力，Muijderman理论考虑了介质可压缩影响，具有更高精度。针对Muijderman方程求解困难问题，采用Adomian分解方法，提出了Muijderman方程近似解。近似解计算量小，误差<5%。利用柯西积分定理求解法，进一步提出了Muijderman方程显式解，没有牺牲解精度，可以指导气膜密封设计。.在一维理论基础上提出了气膜密封二维数值模型，模型与CFD误差<4%，但计算量小。采用该法研究了Muijderman窄槽理论精确性及槽型对气膜密封性能影响。窄槽理论高估了气膜力、泄漏量和气膜刚度，尤其对气膜刚度预测准确性较差。.搭建了动压气膜试验台研究气膜形成机理及影响因素。试验发现在推力盘和瓦块之间产生的气膜使动静端面脱开。推力盘底面中心区域高于边缘区域，使气膜有效面积减少，导致了测量气膜间隙小于理论计算值。提高动环表面质量有利于气膜形成，增加气膜稳定性。提出了一种基于自适应气膜密封的新型汽轮机叶顶复合密封，用以降低汽轮机叶顶泄漏损失和流体激振。针对汽轮机工作环境，研究了介质参数对气膜密封性能影响，比较了理想气体法、对比态定律压缩因子法和IAPWS-IF97法三种过热蒸汽模型，发现介质对气膜密封性能影响较小。建立了基于自适应气膜密封的汽轮机叶顶泄漏三维CFD模型，分析了复合密封泄漏损失及其对气动损失影响，研究了复合密封动力学特性和动环变形对气膜间隙影响。复合密封具有较高流动阻力，降低了叶顶泄漏及由泄漏引起的效率损失。增加密封环面积和弹簧刚度，能够提高静环跟随能力，增强气膜稳定性。增加动环厚度能够提高动环强度，减少结构变形对气膜间隙影响。叶顶气膜密封为解决密封增效减振问题提供了新思路，是提高透平机械效率的一种潜在途径。

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