间隙射流对端壁冷却和传热特性影响的研究

Effects of Slot Purge Flow on Cooling and Heat Transfer Characteristics of End-Wall

关键词:  间隙射流  气膜冷却  端壁传热  数值模拟

Key words:  Slot purge flow  Film cooling  End-wall heat transfer  Numerical simulation

摘要:

采用数值求解三维Reynolds-averaged Navier-Stokes(RANS)方程和[k-ω]湍流模型，研究了间隙射流对燃气轮机叶片端壁冷却和传热特性的影响。通过数值结果与实验数据的比较，验证了数值方法的正确性。在此基础上，研究了间隙射流质量流量比、间隙射流角度对端壁流动结构、气膜冷却性能以及传热特性的影响规律。结果表明，受到端壁二次流结构的限制，冷却气体主要集中在叶片前部吸力面侧。当间隙射流质量流量比小于1%时，会发生主流入侵现象，从而削弱前缘马蹄涡，并且会增加通道喉部区域的热负荷；随着质量流量比的增加，端壁气膜覆盖面积增大，而当射流质量流量比大于1%时，主流入侵现象消失，间隙射流将增强前缘马蹄涡，提高端壁前部的传热，并且减少端壁前部热负荷。随着间隙射流角度的增加，射流引起的分离涡增强，导致端壁前部的传热增强，而端壁气膜有效度降低，端壁热负荷增加。特别是在质量流量比为1.5%时，射流角度从30°增大到90°时，端壁平均气膜有效度减小53.4%。

Abstract:

The effects of the slot purge flow on the cooling and heat transfer characteristics of a gas turbine blade end-wall were numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with [k-ω] turbulence model. Upon numerical validation with experimental data，the effects of mass flow ratio (MFR) and orientation of the slot purge flow on flow structure，film cooling effectiveness and heat transfer of the end-wall were numerically analyzed. The results indicate that the coolant is mainly restricted to fore part of the passage near the suction side due to the effect of secondary flow near the end-wall. When the MFR of the slot purge flow is less than 1%，the main flow can ingest into the slot to suppress the horseshoe vortex (HSV) and the thermal load near the throat of the passage is enhanced. While with the increment of the MFR，the area of region covered by coolant increased，and when the MFR is larger than 1%，the ingestion of the main flow disappeared and the slot purge flow would enhance the HSV and the end-wall heat transfer of the fore part of the passage. In addition，the thermal load of fore part of the end-wall is reduced owing to the slot purge flow. With the increment of the purge flow orientation，the separation vortex caused by the purge flow become intense to enhance the heat transfer of fore part of the end-wall，the film cooling effectiveness of the end-wall is also reduced，therefore the thermal load of the end-wall is enhanced. Especially at MFR=1.5%，when the ejection angle increased from 30° to 90°，the end-wall average film cooling effectiveness is reduced by 53.4%.