Three-Dimensional Bursting Phenomena in Meander Channel

Experiments were conducted in a U-shaped open-channel flume with the intention of investigating the bursting phenomena in the meander channel. The experimental results of the secondary flow fields and the Reynolds shear stress distributions show that the velocity and velocity fluctuation in the transverse direction are not negligible. Moreover, the bursting process is investigated using the three-dimensional quadrant analysis, which is more accurate than using the traditional two-dimensional quadrant analysis for the meandering channel. It is obtained from the experimental results that the internal group of events occurs more frequently than the external group, particularly the internal ejection and internal sweep events. In addition, the transition probabilities of the movements, which are defined as the changes of events from the current situation to the next situation in a time series, show that the stable organizations of events are the most possible movements, whereas the cross organizations of events have the least possible movements.

涡轮导叶压力面分区域复合角气膜冷却特性

针对通道二次流造成涡轮叶片压力面气膜轨迹发生偏转的现象,提出了沿展向分区域布置复合角的设计概念。以高压涡轮导叶HS1A为研究对象,采用数值模拟的方法,在出口雷诺数为2.3×10^(5)的工况下,分析了二次流、复合角和吹风比对气膜冷却特性的影响。结果表明:近端区二次流产生的径向潜流具有促进气膜展向覆盖的能力,相较于叶中区提高了气膜孔出口下游的冷却效率,但也会加剧射流和主流的掺混,减小气膜的有效覆盖长度;针对不同展向区域的二次流大小,精细化布置各区域的气膜孔复合角,可以将气膜轨迹的偏转角度全部修正为0°,同时将平均气膜冷却效率提升了10.42%;复合角冷却模型在吹风比为0.5~1.0时具有较好的范围适用性,吹风比增大至1.3时气膜轨迹会发生反向偏转。

涡轮叶片吸力面双排分区复合角气膜冷却特性

通道二次流作用下,涡轮叶片吸力面气膜轨迹呈收缩状从叶片两端朝叶中偏转。针对该问题,本文设计了高压涡轮叶片吸力面双排分区域复合角气膜冷却模型,并采用数值模拟的方法,分析了二次流和复合角对气膜冷却特性的影响。结果表明,在近端区,叶片上游孔排SS1形成的气膜受马蹄涡的作用偏转较小,叶片下游孔排SS2形成的气膜受较强通道涡的影响偏转角远大于上游气膜;在叶片吸力面增加朝向端壁的复合角设计,可以改善气膜覆盖的均匀性,复合角增大至30?左右时,可以消除射流的脱壁现象,最大复合角工况相比于简单角工况的展向平均气膜冷却效率提高了13.9%。