汽轮机叶顶间隙泄漏流的不稳定特性及其诱导汽流激振研究

The necessary clearance between the blade tip and the cylinder wall can cause the blade tip leakage losses in steam turbine flow passage, due to the leakage flow from the high-pressure side of the blade tip to the other side. The blade tip leakage losses lead to decrease the efficiency of stage, and influence on the economy of steam turbine. At the same time, the safe operation of steam turbine with advanced parameter and large capacity is also threatened seriously by the steam-excited vibration force, which is caused by the unsteady vortex motion of the tip leakage flow in the uneven circumferential clearance. However, there is a lack of systematic research on the unsteady flow characteristics of blade tip leakage vortex and the induced steam-excited vibration force. In this study, based on the theory of vortex motion, the formation reason of the blade tip leakage flow pattern and the mutual interference regularity of leakage vortexes are researched by the means of numerical simulation and visualization experiment. The formation mechanism of blade tip leakage losses, the unsteady characteristics of tip leakage vortex movement and the induced law of pressure fluctuation at the blade tip clearance can be illuminated. The relationship between the pressure fluctuation and the steam-excited vibration can be established. The aim of this study is to reveal the physical mechanism of the blade tip leakage flow and leakage vortex, and analyze the mechanism of leakage vortex induced steam-excited vibration. The research results will fall the firm theoretic foundation for the decrease of blade tip leakage losses and the control of steam-excited vibration at the blade tip clearance.

在汽轮机的通流部分，动叶片与汽缸壁之间不可避免的存在间隙，致使蒸汽由高压侧向低压侧泄漏，形成叶顶间隙泄漏损失。叶顶间隙泄漏损失是导致级效率下降的主要损失，影响着汽轮机的经济性。同时，周向不均匀叶顶间隙泄漏的非定常涡动诱导的汽流激振力也严重地威胁着高参数、大容量汽轮机的安全运行。然而，对汽轮机叶顶间隙泄漏涡的非定常流动特性及其诱导汽流激振的机理还缺乏系统的研究。本项目基于涡运动理论，采用数值模拟并辅以可视化实验手段，研究汽轮机叶顶间隙泄漏流动形态的成因以及泄漏涡系间相互干涉的规律，确定叶顶间隙泄漏流动损失的形成机制、叶顶间隙泄漏涡运动的不稳定特性及其诱导叶顶间隙内压力脉动的规律，建立叶顶间隙泄漏涡引起的压力脉动特性与汽流激振之间的关系，旨在揭示汽轮机叶顶间隙泄漏流与泄漏涡的物理机制和泄漏涡诱导汽流激振产生的机理，为减小叶顶间隙泄漏损失及抑制叶顶间隙汽流激振奠定坚实的理论基础。

在汽轮机的通流部分，动叶片与汽缸壁之间不可避免的存在间隙，受级前后的压差作用，蒸汽由高压侧向低压侧泄漏，形成叶顶间隙泄漏损失，影响着汽轮机的经济性。同时，周向不均匀叶顶间隙泄漏的非定常涡动诱导的汽流激振力也严重地威胁着高参数、大容量汽轮机的安全运行。然而，对汽轮机叶顶间隙泄漏涡的非定常流动特性及其诱导汽流激振的机理还缺乏系统的研究。本项目基于涡运动理论，采用数值模拟并辅以可视化实验手段，研究汽轮机叶顶间隙泄漏流动形态的成因以及泄漏涡系间相互干涉的规律，确定叶顶间隙泄漏流动损失的形成机制、叶顶间隙泄漏涡运动的不稳定特性及其诱导叶顶间隙内压力脉动的规律，建立叶顶间隙泄漏涡引起的压力脉动特性与汽流激振之间的关系。研究结果表明，汽封腔室内的大涡和围带壁面附近的小涡是蒸汽动能的主要耗散形式。转子偏心、密封间隙、密封齿数的改变均会导致涡的抬升、下降以及分离和破碎。泄漏流和主流掺混产生的损失是泄漏损失的主要成分。叶顶间隙增大，掺混损失增加，最大熵增区域向中间叶高偏移。叶顶间隙泄漏流诱导汽流激振力的主要原因是间隙不均导致泄漏流旋转涡动和压力分布不均引起的。随着转子偏心距的增大，径向激振力的均值增幅较明显，切向汽流激振力的产生主要与叶顶间隙泄漏流旋转速度大小、方向和径向间隙不均匀程度有关。通过上述研究，本项目揭示了汽轮机叶顶间隙泄漏流与泄漏涡的物理机制和泄漏涡诱导汽流激振产生的机理，为减小叶顶间隙泄漏损失及抑制叶顶间隙汽流激振奠定坚实的理论基础。