导叶展弦比对部分进气涡轮性能影响的数值研究

Numerical Investigation on the Effect of Stator Aspect Ratio on Aerodynamic Performance in a Partial Admission Turbine

本文针对导叶展弦比对部分进气涡轮性能的影响进行了数值研究。结果表明:转子前缘靠近导叶吸力面边界处流动发生分离形成分离涡,使得损失增加;展弦比增加能增加进气区转子前缘靠近导叶吸力面处主流速度,进而降低分离涡强度并降低部分进气效应对进气区中心区域流动的影响,改善进气扇区中心区域流动,从而减少损失提升效率。与此相反,叶高、稠度不变时展弦比增加使得叶片数增加,叶型损失增加,且进气度越大,叶型损失增加量越大。当进气度小于50%时,进气扇区较小,展弦比增加诱发的分离涡强度降低的作用效果明显强于叶片数增加的影响,二者的综合作用使得涡轮效率得到提升;当进气度大于50%以后,分离涡对进气扇区中心区域的影响降低,分离涡强度的降低仅能改善进气区边界靠近导叶吸力面处的流动状态,但此时叶片数增加导致的叶型损失会显著增加,二者的综合作用导致涡轮效率提升的幅度降低。

The influence of stator aspect ratio on aerodynamics and performance of a partial admission turbine is analyzed numerically. Results show that flow separation occurs at rotor leading edge close to suction side of stator. The losses are increased since a new vortex arises in that region. The velocity at the rotor leading edge close to suction side of stator is raised as the stator aspect ratio increase, and then the intensity of the vortex is reduced, which weaken the effect of partial admission on the performance of central channel. The flow conditions of central channel are ameliorated. All of those reasons improve the performance of the turbine. On the contrary, with constant blade height and solidity, the blade numbers of stator increase with the increasing of aspect ratio. It results in the increase of the blade profile losses. As the admission degree is less than 50%, the decline of separating vortex intensity induced by increases of the stator aspect ratio plays a dominant effect, although the blade profile losses are increase due to the increasing of the blade numbers. It causes that the efficiency of turbine increases with the increase of stator aspect ratio. As the admission degree is more than 50%, the increment of the turbine efficiency is lower than the one with the admission degree less than 50%, although the turbine efficiency increases with the increase of stator aspect ratio.It is because that the negative impact of the separation vortex on the performance of the central admitted channelis weaker compared to the one with admission degree less than 50%. It causes that the decline of the vortex intensity just ameliorates the flow conditions of the channel boundary close to suction side of stator. So the increment of turbine efficiency induced by reduces of vortex intensity is less than the one with admission degree less than 50%. However, the increase in the amount of blade profile losses is higher than the one with admission degree less than 50%. The combination of two effects reduces the increment of the turbine efficiency.