## 5 Results and Discussions  
### Analysis of the Optimization Results  
Figure 9 shows the original and optimized compressor performance maps. As can be seen in Figure 9, compared with the original compressor the optimized configuration has a higher stall margin, which is about 2.69% higher than that of the original compressor, and the adiabatic efficiency also improves by 0.12%.  
To illustrate the information of the optimized blade geometry relative to the original blade geometry, we take the second-stage rotor and the second-stage stator as examples. Figure 10 shows the variation of the second-stage rotor surface of the optimized compressor relative to the original compressor. Among them, Figure 10a shows a three-dimensional modeling diagram of the original second-stage rotor and the optimized second-stage rotor. Figure 10b shows the circumferential fluctuation amount A of the optimized second-stage rotor compared with the original second-stage rotor, where positive values indicate changes in the circumferential position in the direction of the pressure surface and negative values indicate changes in the circumferential position in the direction of the suction surface. It can be seen that the entire second-stage rotor exhibits a positive value, which means the optimized compressor rotor changes in the circumferential position in the direction of the pressure surface. Among them, the area with the largest amplitude of positive values is concentrated near the leading edge in the hub region. This can also be seen from Figure 10a. Besides, the region from the middle section to the trailing edge has the smallest amplitude of positive values, which means that  
Figure 8: Optimization process of the highly loaded compressor.  
Figure 9: Original and optimized compressor performance maps. (**a**) Adiabatic efficiency at the different normalized mass flow; (**b**) total pressure ratio at the different normalized mass flow.  
the curvature near the leading edge is greater than that of the middle section, thus the field structure in chord-wise and span-wise direction may be changed.  
Figure 11 shows the variation of the second-stage stator surface of the optimized compressor relative to the original compressor. However, it should be noted that the positive values of fluctuation amount A indicate changes in the circumferential position in the direction of the suction surface and negative values indicate changes in the circumferential position in the direction of the pressure surface. This is just the opposite of the rotors. As can be seen in Figure 11b, the changing trend of the second-stage stator is different from that of the second-stage rotor. The area with the largest amplitude of negative values is concentrated near the leading edge above the 50% span region. It means that the stator has a larger turning angle above the 50% span region; this can also be seen from Figure 11a. More analysis of the structure of the flow field is shown below.  
Figure 11: Comparison of suction and pressure surface of the original and optimized second-stage stator. (**a**) Three-dimensional modeling diagram of the original second-stage stator and the optimized second-stage stator; (**b**) the circumferential fluctuation amount A of the optimized second-stage stator compared with the original second-stage stator.  
Figure 10: Comparison of suction and pressure surface of the original and optimized second-stage rotor. (**a**) Three-dimensional modeling diagram of the original second-stage rotor and the optimized second-stage rotor; (**b**) the circumferential fluctuation amount A of the optimized second-stage rotor compared with the original second-stage rotor.