# Numerical Study on Cooling Performance of a Steam-Cooled Blade Based on Response Surface Method
## 3 Effect of Working Parameters on the Cooling Performance of the Blade
### Influence of Mainstream Inlet Temperature  
Figure 8 gives the influence law of the mainstream inlet temperature on the cooling efficiency of the steam cooled blade. In the figure, the horizontal coordinates \(-1\)-\(1\) are the relative axial chord length of the steam cooled blade, \(-1\)-\(0\) means the pressure surface of the blade, and \(0\)-\(1\) means the suction surface of the blade. When studying the effect of single working parameters on the cooling efficiency of steam cooled blade, the rest of the working parameters are in the medium value, such as studying the effect of the mainstream inlet temperature, the mainstream outlet pressure is \(140\) kPa, the mainstream inlet to outlet pressure ratio is \(1.4\), the temperature ratio of steam to mainstream is \(0.65\), the flow ratio of steam to mainstream multiplied by \(100\) is \(5.5\), the same below. From Figure 8a-c, it can be seen that the cooling efficiency of the steam cooled blade tip position is higher than that of the blade root position, which is because the steam flows into the blade from the blade tip and out from the blade root. The leading edge of the blade is directly impacted by the high temperature of the incoming flow, so it has a poor cooling effect, and the cooling efficiency is in the range of \(0.25\)-\(0.35\). The highest cooling efficiency region is in the mid-chord region of the tip of the steam-cooled blade, and the cooling efficiency can reach about \(0.65\). The tip and root positions of the trailing edge of the steam-cooled blade have the worst cooling effect, and the cooling efficiency is in the range of \(0.15\)-\(0.2\). Overall, the cooling effect of the pressure surface of the steam-cooled blade is better than that of the suction surface, which is probably due to the fact that the flow velocity of the suction surface is higher than that of the pressure surface and there is a reverse pressure gradient on the suction surface of the blade, so that the heat of the mainstream can be transferred to the surface of the blade more easily. In addition, from Figure 8a-c, it can be shown that the cooling efficiency distribution on the surface of the steam-cooled blade hardly changes when the mainstream inlet temperature is changed. This also indicates that the influence of the mainstream inlet temperature on the temperature nonuniformity of the steam cooled blade is also not significant. As can be shown in Figure 8d, the influence of mainstream inlet temperature on the average cooling efficiency and temperature non-uniformity of air-cooled and steam-cooled blade is not significant, and the average cooling efficiency of steam-cooled blade is \(15.28\)-\(15.85\)% higher compared with air-cooled blade at different mainstream inlet temperature, which is about \(15.59\)% higher on average. It is also worth noting that steam-cooled blade has better cooling efficiency than air-cooled blade, but at the same time the temperature distribution on the blade surface is more uneven. At different  
Figure 7: Surface streamline of the blade: (**a**) suction surface of the blade; (**b**) pressure surface of the blade. mainstream inlet temperature, the steam-cooled blades are 21.96-22.73% higher than the air-cooled blades, with an average of about 22.31% higher. Figure 9 shows the influence of the mainstream inlet temperature on the distribution of the dimensionless temperature of the steam cooled blade. From Figure 9a-c, it can be found that when the rest of the working parameters are kept constant and the mainstream inlet temperature increases, the distribution of the dimensionless temperature on the surface of the steam-cooled blade is in the range of 0.79-0.92. The distribution of the dimensionless temperature of the steam cooled blade is just opposite to the distribution of the cooling efficiency, that is, the region with high cooling efficiency has a lower distribution of the dimensionless temperature, while the region with higher dimensionless temperature has a lower distribution of the cooling efficiency.