计及机匣相对运动的涡轮叶片叶顶凹槽流动研究

Experimental and numerical study of squealer tip flow field considering relative casing motion

叶尖泄漏流是造成航空发动机涡轮内部损失的重要因素,而凹槽叶尖是控制叶尖泄漏流的有效手段,准确了解凹槽内的流动结构有助于认识泄漏流的流动规律和泄漏损失的物理机制。为了详细研究考虑机匣相对运动时叶尖凹槽腔内流动结构变化及其对泄漏流的影响,搭建了可模拟机匣相对运动的低速平面叶栅实验台,该实验台可以进行不同叶型、不同叶顶结构以及不同攻角等因素的研究。采用PIV技术设计了一种可以在机匣相对运动时对凹槽腔内流动进行测量的可视化测量方法。使用该测量方法捕捉到了凹槽腔内旋涡的流动结构,结合数值结果分析了不同机匣运动状态下凹槽腔内流动结构的演化过程,结果表明:刮削涡在凹槽腔内形成类似气动篦齿的封严效果,减小了间隙出口有效流通面积,降低了凹槽叶尖的射流系数,从而达到了控制泄漏流动的目的;选择合适的负荷分布和凹槽几何能够提升刮削涡的堵塞效果并扩大控制范围;均匀加载叶片使用叶尖凹槽时控制泄漏流的效果更加明显;径向间隙的大小直接影响叶顶凹槽内部流动结构的产生和演化,从而改变凹槽叶尖控制叶尖泄漏的效果。

The tip leakage flow is an important factor that causes the internal loss of the aeroengine turbine.The squealer tip can effectively control the tip leakage flow.Accurate understanding of the tip leakage flow structures in the cavity contributes to the understanding of the flow characteristics of the leakage flow and the physical mechanism of the leakage loss.In order to study the change of flow structures in the tip cavity when considering the relative casing motion and the effect on the leakage flow,a low-speed turbine cascade testing facility is built that can model the relative casing motion.The test facility can study factors such as blade profiles,different tip structures,and different incidence angles.A visual testing method of Particle Image Velocimetry(PIV)is proposed to obtain the complex flow structures within the tip cavity.The measurement method developed can obtain the complex flow field and successfully capture the scraping vortex in the tip cavity.In addition,the evolution of the flow structures in the tip cavity is analyzed with the help of numerical results under different casing motion conditions.An aerolabyrinth like sealing effect is formed by the scraping vortex.This sealing effect reduces the equivalent flow area at the gap outlet and diminishes the discharge coefficient of the squealer tip,therefore finally achieving the purpose of controlling the leakage flow.Choosing the appropriate blade load distribution and cavity geometry can improve the clogging effect and expand the control range of the scraping vortex.Mid-loaded blades have a more obvious effect on controlling the leakage flow when using the cavity tip.The tip gap height affects the generation and evolution of the flow structure in the tip cavity by which changes the effect of controlling the leakage flow.