热载与进口气流条件对柱肋通道换热的影响

Effects of Heat Load and Inlet Flow Conditions on Heat Transfer in Channels with Pin Fin Arrays

关键词:  叶片冷却  柱肋通道  流动换热  热载  进口气流条件

Key words:  Blade cooling  Channels with pin fin arrays  Flow and heat transfer  Heat load  Inlet flow conditions

摘要:

目前关于燃气涡轮叶片冷却的实验研究多数是在常温常压进口气流和低壁温条件下进行的，而实际燃气涡轮叶片的冷却气流为来自于压气机的高温高压空气，且涡轮叶片壁面热载（定义为加热壁面壁温与冷却气流进口温度之比）很高。为了掌握热载与进口气流条件对于涡轮叶片尾缘内部冷却通道的冷却效果的影响，在考虑空气物性随温度变化的情况下，采用数值模拟方法进行了相关的计算和分析。计算选取了两种进口气流条件（常温常压、高温高压），热载为1.1～1.9，进口气流雷诺数为5×10³～1×10⁵。计算结果表明，进口气流雷诺数一定的情况下，随着热载的增大，通道内换热能力降低，流动阻力系数增大；与常温常压进口气流条件相比，高温高压进口气流条件导致通道努塞尔数降低，并且努塞尔数在高热载条件下的降低更为显著；在进口气流雷诺数为6×10⁴的条件下，高温高压进口气流、热载为1.9的条件下通道的努塞尔数比与常温常压进口气流条件、热载为1.1条件下通道的努塞尔数降低了15.8%，且随着进口气流雷诺数的增加，通道换热的削弱程度进一步增大。本文的研究表明，涡轮叶片的冷却设计必须考虑叶片冷却的实际条件，并对实验数据结果进行合理修正。

Abstract:

Most researches on the gas turbine’s blade cooling were carried out experimentally at conditions of atmospheric air inlet and low wall temperature. However， the cooling air for the actual turbine blade is from compressor with high temperature/pressure and the heat load of the blade （defined as the ratio of isothermal blade wall temperature to the cooling air inlet temperature） is high. To understand the effects of the air inlet and heat load conditions on the cooling performance of internal cooling channels in turbine blade trailing edge with pin fin arrays， a CFD simulation study was carried out with the consideration of the variation of air thermo-physical properties. There were two air inlet flow conditions： high air inlet temperature/pressure and atmospheric air inlet temperature/pressure. Heat loads were set from 1.1 to 1.9. Reynolds numbers （Re） of the air inlet flow were set from 5×10³ to 1×10⁵. The numerical results show that with the increase of heat load， the heat transfer capacity of the channel decreases and the friction factor increases with the same Re of air inlet flow. In comparison with the atmospheric air inlet conditions， high air inlet temperature/pressure conditions cause the decrease of the Nusselt number （Nu） in the channel， and with the increase of heat load， the decrease of Nu becomes larger. With the Re of 6×10⁴， the Nu of the channel at high air inlet temperature/pressure conditions and heat load of 1.9 decreases by 15.8% in comparison with that at atmospheric air inlet conditions and heat load of 1.1. With the increase of Re of air inlet flow， the decrease of heat transfer in channel becomes larger. These results propose that the experimental data need to be modified during the design of actual blade’s cooling with the consideration of actual cooling conditions of turbine blade.