高湍流度时全气膜涡轮叶片表面冷却和换热特性的实验研究

Experimental Study on Film Cooling and Heat Transfer Characteristics of a Fully-Cooled Turbine Vane at High Turbulence Intensity Condition

关键词:  高主流湍流度  全气膜叶片  气膜冷却效率  换热系数比  实验

Key words:  High mainstream turbulence intensity  Fully-cooled vane  Film cooling effectiveness  Heat transfer coefficient ratio  Experiment

摘要:

为获得高主流湍流度时全气膜涡轮叶片表面的冷却和换热特性，在跨声速风洞中实验研究了质量流量比（MFR）和主流雷诺数（Re）对叶片表面气膜冷却效率和换热系数比的影响。在叶片前缘布置了5排圆形孔，在吸力面和压力面分别布置了3排和6排圆形孔，实验结果由嵌入在叶片中截面的热电偶测得。实验中基于弦长的主流雷诺数的范围为3.0×10⁵~9.0×10⁵，叶栅出口马赫数Ma为0.8， MFR的范围是5.5%~12.5%，主流湍流度Tu为14.7%。实验结果表明：主流雷诺数升高显著增强了叶片表面的换热，使层流边界层到湍流边界层的转捩位置提前。对于吸力面S/C>0.2的区域（S/C为当地弧长与弦长之比），气膜冷却效率受MFR影响明显，当MFR大于7.7%时提高MFR会导致气膜冷却效率降低；该区域的换热系数比在中低雷诺数时受MFR影响较小，在高雷诺数时随MFR升高而升高。压力面S/C< -0.7区域的气膜冷却效率随MFR升高而升高，-0.7<S/C<-0.4区域的气膜冷却效率受MFR影响较小，对于整个压力面而言，MFR升高提高了叶片表面的换热系数。相对于叶片其它区域，压力面后半段区域和吸力面的气膜冷却效率受雷诺数影响较大。

Abstract:

An experiment was performed in the transonic wind tunnel to obtain the film cooling and heat transfer characteristics of a fully cooled turbine vane at high mainstream turbulence intensity condition. The effect of mass flow ratio (MFR) and Reynolds number (Re) on the film cooling effectiveness and heat transfer coefficient was studied. Five rows of cylindrical holes were arranged on the leading edge, three rows and six rows of cylindrical holes were provided on the suction side and pressure side, respectively. The experimental results were measured by the thermocouples embedded in the middle span of the vane. In the experiment, the inlet Reynolds number based on the chord length ranged from 3.0×10⁵ to 9.0×10⁵, the exit Mach number of the cascade was 0.8, the mass flow ratio varied from 5.5% to 12.5% and the mainstream turbulence intensity was 14.7%. Experimental results show that the increase of inlet Reynolds number significantly strengthens the heat transfer on the vane surface and leads to advanced laminar-to-turbulent layer transition position. In the region of S/C >0.2 on the suction side (S/C is the ratio of local arc length to the chord length), the film cooling effectiveness is significantly affected by MFR, increased MFR leads to decreased film cooling effectiveness when MFR is larger than 7.7%. The heat transfer coefficient of this region is slightly affected by MFR at low and medium Reynolds number conditions, while it increases with the increase of MFR at high Reynolds number condition. The film cooling effectiveness in the region of S/C<-0.7 on the pressure side increases with MFR increasing, while it is less affected by MFR for -0.7<S/C<-0.4. Increased MFR results in enhanced heat transfer coefficient on the entire pressure side. Compared with other regions of the vane surface, the film cooling effectiveness on the suction side and the rear half of pressure side is obviously affected by the Reynolds number.