# Investigation of the Effects of Different Working Fluids on Compressor Cascade Performance
## 4 Performance Analysis
### Effect of Physical Properties on Coefficient of Total Pressure Loss  
The correlation of the coefficient of total pressure loss and specific heat ratio at matching Reynolds number and Mach number is presented in Figure 7. Compressor cascade using higher heat ratio working fluid has a greater coefficient of total pressure loss. Helium's coefficient of total pressure loss and carbon dioxide is calculated using Equation (13) as the coefficient of total pressure loss of air is known. Relative prediction error is less than 5%, which is enough to meet the engineering demand. Mach number and Reynolds number also have an important effect on compressor cascade total pressure loss. As presented in Figure 7, the coefficient of total pressure loss of compressor cascade increases significantly with the increase of Reynolds number and Mach number. As for the influence of attack angles on the coefficient of total pressure loss, the coefficient of total pressure loss of compressor cascade first decreases and then increases with the increase of attack angle and has minimum total pressure loss coefficient at \(-3^{\circ}\)attack angles.  
The distribution of the coefficient of total pressure loss over blade height is presented in Figure 8. As shown in Figure 8, at a certain attack angle and Mach number, coefficient of total pressure loss of compressor cascade increases with the increase in specific heat ratio of working fluid in the whole blade height. At identical attack angle, the coefficient of total pressure loss in the compressor cascade increases obviously by Mach number. Moreover, at the same time, on the higher Mach number, the variance in the coefficient  
Figure 6: Static pressure coefficient (Cp) distribution at 98% span.  
Figure 7: The correlation among coefficient of total pressure loss and Reynolds number, Mach number, specific heat ratio.  
of total pressure loss in compressor cascade using dissimilar working fluid is clearly visible. At the range 0%-20% blade height, the energy dissipation is intensified due to the effect of corner separation, it leads to an increase in difference in the coefficient of total pressure loss with different working fluids. To a certain extent, it reflects that fluid specific heat ratio affects total pressure loss by effecting the energy dissipation of working fluid. When different working fluids are used in compressor cascades at similar Mach number, variance of total pressure loss coefficient along blade height increases with an increase in attack angle.  
Figure 9 shows the contour of coefficient of total pressure loss of compressor cascade with carbon dioxide and helium at a different plane. As shown in Figure 9, in all planes the  
Figure 8: Distribution of coefficient of total pressure loss over blade height.  
size and strength of the separation vortices of compressor cascade with helium are higher than carbon dioxide. As a result, total pressure loss coefficient of compressor cascade with helium is significantly higher than carbon dioxide, and the larger the vortex separation scale and intensity are, the more obvious the difference of coefficient of total pressure loss.