# 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 to Outlet Pressure Ratio  
Figure 12 presents the influence law of mainstream inlet to outlet pressure ratio on the cooling efficiency distribution of the steam-cooled blade, from Figure 12a-c, it can be learned that when the rest of the working parameters are in the middle value and kept constant, the cooling efficiency distribution of the steam-cooled blade surface is in 0.20-0.62 when the mainstream inlet to outlet pressure ratio is 1.3-1.5. When the mainstream inlet to outlet pressure ratio increases, the cooling efficiency of the steam-cooled blade surface increases, that is the area of the low cooling efficiency area of the trailing edge of the steam-cooled blade reduces, and the area of the high cooling efficiency area of the middle chord area of the blade increases, while the cooling efficiency distribution of the leading edge of the blade changes very little. This may be due to the pressure ratio of the mainstream inlet to outlet increase on the blade leading edge of the airflow impact is not large, but it will make the airflow velocity of the blade chord area and trailing edge increase, which will increase the blade surface heat transfer efficiency, thus increasing the cooling efficiency of the blade. In the relative axial chord length \(-\)0.2 and 0.9 region blade cooling efficiency increased by about 0.8% and 16.9%, which indicates that the pressure ratio of the mainstream inlet to outlet on the cooling efficiency of the trailing edge of the steam-cooled blade is greater than the leading edge and the middle chord area. In addition, the temperature distribution on the surface of the steam-cooled blade is more uniform with the increase of the pressure ratio of the mainstream inlet to outlet, which indicates that the pressure ratio of the mainstream inlet to outlet reduces the temperature non-uniformity of the steam-cooled blade. The average cooling efficiency and temperature non-uniformity of the steam-cooled blade increased by 5.92% and decreased by 4.09% with the increase of the pressure ratio of the mainstream inlet to outlet, respectively. From Figure 12d, it can be seen that the average cooling efficiency of steam-cooled blade is about 14.06-17.81% higher than that of air-cooled blade in the range of working parameters, with an average of about 15.71% higher; the temperature non-uniformity of the former is about 21.49-23.27% higher than that of the latter, with an average of about 22.21% higher.  
Figure 11: Influence of mainstream outlet pressure on dimensionless temperature distribution: (a) \(p_{\rm{go}}=\) 120 kPa; (b) \(p_{\rm{go}}=\) 140 kPa; (c) \(p_{\rm{go}}=\) 160 kPa; (d) Variation law of the mean value.  
Figure 12: _Cont._Figure 13 presents the influence law of mainstream inlet to outlet pressure ratio on the dimensionless temperature of steam-cooled blade, from Figure 13a-c, it can be observed that when the mainstream inlet to outlet pressure ratio is 1.3-1.5, the dimensionless temperature distribution on the surface of the steam-cooled blade is 0.78-0.93. When the mainstream inlet to outlet pressure ratio increases, the area of the high dimensionless temperature region at the trailing edge of the steam-cooled blade slightly decreases, and the area of the low dimensionless temperature region at the middle chord of the blade increases. while the variation of the dimensionless temperature distribution at the leading edge of the blade is quite narrow. After calculation, it can be seen that when the mainstream inlet to outlet pressure ratio increases from 1.3 to 1.5, the average dimensionless temperature of the steam-cooled blade decreases by 0.93%. From Figure 13d, it can be found that the average dimensionless temperature of both air-cooled and steam-cooled blade decreases with the increase of the pressure ratio of the mainstream inlet to outlet, but the steam-cooled blade is about 2.03-2.43% lower compared with the air-cooled blade at the same pressure ratio of the mainstream inlet to outlet, and the average is about 2.20% lower.