超高负荷低压涡轮叶片前缘型态与上游尾迹耦合机理研究

In a request for higher thrust-to-weight ratio, morden high bypass ratio turbofan engine tend to reduce the number of stages and blades of low-pressure (LP) turbine, which prompted the development of ultra-high-lift design of LP turbine blades (Zweifel number 1.4 or above).Hower, with the further elevation of the load of low-pressure turbine blades, the suction surface boundary layer encounters stronger adverse pressure gradient. At the same time LP turbines operate at low Reynolds number in high-autitude cruise condition which makes the blade suction surface boundary layer growing thick and the flow is prone to separate, leading to increased losses, even under the influences of unsteady wakes. Different leading-edge shapes affect the sucetion surface gradient which makes the differences of the boundery layer momentum thickness of the front portion of blades. In addition, the leading-edge shape influences the wake-induced transition by changing the characteristics of unsteady wakes. Basing on the mechanism of the wake-passing/blade leading-edge interaction affecting the separation and transition of boundary layer, it is useful to optimize the parameters of wake and tailor the leading edge for elevating the performance of blade. It supplies the ultra-highly-loaded LP turbine blade design technology for the next generation engine with high thrust-to-weight.

现代高涵道比涡扇发动机中，为了追求更高的推重比，减少低压涡轮级（叶片）数已经是必然的趋势，这促使了低压涡轮叶片向超高升力（Zweiful数1.4以上）的设计方向发展。叶片负荷的提高使得吸力面逆压梯度不断地增加，再加上低压涡轮在高空巡航状态下工作时雷诺数较低，即使在引入了上游尾迹的扫掠作用后，超高负荷低压涡轮叶片内仍然不可避免地存在着流动分离，损失急剧增加。叶片前缘几何形状一方面影响叶片前部附面层的动量厚度，另一方面影响尾迹的传输特性以及尾迹诱导湍流斑的形成和尾迹诱导转捩过程。本项目拟基于上游尾迹周期性扫掠与叶片前缘相互作用对超高负荷低压涡轮叶片吸力面附面层分离及转捩过程影响机制的认识，通过优化配置上游尾迹，适当选择叶片前缘形状，实现对吸力面附面层的调控，借助二者的耦合作用最大限度地提升叶片性能，为下一代高推重比发动机超高负荷低压涡轮的设计提供基础性技术支撑。

超高负荷低压涡轮叶片在低Re数工况下不可避免地出现流动分离，损失急剧增加。本项目通过叶栅实验和数值模拟的方法研究了均匀来流条件下以及上游尾迹周期性扫掠下叶片前缘形状和粗糙度对超高负荷低压涡轮叶片吸力面附面层分离、转捩流动的影响机理，通过优化配置上游尾迹，适当选择叶片前缘形状和前缘粗糙度配置，实现对吸力面附面层的调控，借助二者的耦合作用最大限度地提升叶片性能。针对不同的叶片前缘设计，得到了最优的尾迹扫掠频率，以及影响最优扫掠频率的因素。