扇形与平面叶栅内高负荷叶片的换热特性实验研究

为了探究扇形与平面叶栅条件下,高负荷叶片的外换热特性,采用瞬态液晶测量技术,测量了雷诺数(Re)、湍流强度(Tu)对扇形叶栅(曲端壁)的小展弦比高负荷涡轮叶片表面努塞尔数(Nu)的影响,并与平面叶栅(直端壁)进行了对比。结果表明,曲端壁相较于直端壁增加了21.5°的径向进气角以及上下端壁曲率不同,从而导致换热沿叶高的不对称分布。雷诺数增大,叶片各位置的换热明显增强,吸力面边界层转捩点位置不断向前缘靠近,雷诺数对直端壁的影响大于曲端壁。随湍流强度增大,努塞尔数整体有所升高,吸力面转捩点位置前移,压力面过渡现象明显增强,中弦部分努塞尔数一维特性更为明显,湍流强度对两类端壁的叶片影响类似。在研究低雷诺数或湍流强度对高负荷叶片的换热影响时,可采用直端壁进行简化,而在高雷诺数时,为了保证结果准确性,需在发动机实际扇形叶栅中进行实验。

Experimental Study on Heat Transfer Characteristics of Highly-Loaded Blades Between Sector and Linear Cascade

To explore the overall heat transfer characteristics of highly-loaded blades with sector cascade and linear cascade, the effects of Reynolds numbers(Re) and turbulence intensity(Tu) on the Nusselt number(Nu) of highly-loaded blades with small aspect ratio was measured by using the transient liquid crystal measurement technique with a sector cascade(curved endwall). The results were compared with those of a linear cascade(straight endwall). The results reveal the asymmetric distribution of heat transfer along the blade height. That is because the radial inlet angle is increased by 21.5°of curved endwall compared with straight endwall and the upper and lower endwalls have different curvature of curved endwall. With the increase of Re, the heat transfer at each position of the blade is obviously enhanced, and the transition point of the laminar boundary layer on the suction surface is approaching to the leading edge. The effect of Re on straight endwall is greater than that on curved endwall. With the increase of Tu, the overall Nusselt number(Nu) increases. The transition point on the suction surface moves forward, and the transition phenomenon on the pressure surface is obviously enhanced. The one-dimensional characteristic of Nu on the middle chord is more obvious. Tu has similar effects on the blades of two endwalls. In the study of the influence of low Re or Tu on the heat transfer of highly-loaded blades, the straight endwall can be used for simplification. But in order to ensure the accuracy of high Re, the experiment should be carried out in the real sector cascade of the engine.