Experimental and numerical investigations of tip clearance flow and loss in a variable geometry turbine cascade

Abstract

Variable geometry turbines are widely employed to improve the off-design performance of gas turbine engines; however, there is a performance penalty associated with the vane-end partial gap required for the movement of variable vanes. This paper is a continuation of the previous work and aims to understand the leakage flow and loss mechanisms under the influence of the pivoting axis. Experimental investigations with a variable geometry turbine linear cascade have been conducted for tip gap heights of 1.1% and 2.2% blade spans as well as setting angles of À6 , 0 , and 6 , so as to reveal the three-dimensional clearance flow characteristics associated with partial gaps. Besides, numerical predictions are also carried out to better understand the experimental results. Pressure measurements were performed on the tip endwall as well as on the vane surface, and three-dimensional clearance flow fields downstream of the variable cascade were measured with a five-hole probe. The results show that as the vane setting angle is changed from design to closed, the vane loading increases and tends to be more aft-loaded, thus increasing the tip leakage loss, and vice versa. There are strong interactions between the flow around the pivoting axis and the leakage flow in the vane tip rear part, which leads to a low-pressure region on the tip endwall. The leakage vortex core is made up of the leakage flow in the vane tip rear part at both two tip gap heights, and the leakage vortex core formation process is different from the one in the rotor blade. The present results can provide useful references for the vane-end clearance design of variable geometry turbines.

Advances in variable geometry turbine aerodynamic technology for gas turbines

“…涡轮变几何后, 必须在静叶端部留有间隙并设置 旋转轴 [25] (图4), 以保证静叶的自由转动, 这样就会引 起静叶端区的附加损失, 导致涡轮效率的下降, 同时 也增加了控制系统的复杂性 [13,19] .…”

“…哈尔滨工程大学刘顺隆等人 [26] 图 3 变几何动力涡轮与定几何动力涡轮的性能对比 [21] 图 4 (网络版彩图)可调静叶旋转轴结构 [25] 值得注意的是, 现代船舶燃气轮机动力涡轮大多 在对可调静叶级匹配影响方面, 冯永明等人 [7,22,34] 通过忽略可调静叶端部间隙的影响, 初步数值研究了 由于涡轮级间相互干扰, 可调静叶级的通流特性 变化将显著影响整个变几何涡轮的气动特性 [37] . 高杰 等人 见国外相关公开报道.…”

“…[53] , 这进一步加剧了可调静叶端区泄 漏流动的复杂性. 并且, 当大扩张角端壁可调静叶转 动时, 不仅静叶端部间隙大小和形态发生剧烈变 化 [29,33] , 而且静叶自身出现非零冲角来流, 加之大扩张 角流道特征, 叶片端区表面的流态因而会发生明显改 变, 甚至出现大分离现象 [25] . 此外, 鉴于大扩张角端壁 可调静叶在转动时由于端部间隙形态变化更加剧烈而 很容易发生卡死现象 [29,33] , 虽然通过增大端部间隙可…”

Numerical Research on the Impact of Axial Position of Endwall Suction Slot on Tip Leakage Flow

“…The results of some pieces of literature showed that the performance of compressor and cascade could be improved as the separation flow was controlled by introducing an appropriate clearance size. While a larger clearance size led to the enhancement of the TLF, which would decrease the performance of the compressor (Zuo et al 2011;Chen et al 2012Chen et al , 2013Gottschall et al 2012;Gao et al 2017). In addition, Liu et al (2016a) and Mao et al (2019) explored the effect of tip clearance of the rotors on the performance of a counter-rotating axial flow compressor.…”

Tip leakage flow analysis of an axial turbine under the effect of separation at low Reynolds number

“…6,7 Some combined control technologies at the clearance region have been put forward recently, e.g. casing treatment and blowing, 8 winglet and squealer, 9,10 and honeycomb seal. 11,12 However, the relative motion between the blade and shroud endwall has been neglected in these studies.…”