# Influence of Active Flow Control of Synthetic Jet at
## 5 Influence and Analysis of Synthetic Jet on Compressor Performance
### Internal Flow Analysis of Compressor  
To reveal the influence mechanism of the suction surface jet on the overall performance and stability margin of the compressor, take the near-stall mass flow of the prototype  
Figure 10: Effect of synthetic jet on the total performance of subsonic axial compressor. compressor. As an example, Figure 11 presents the relative Mach number contour at different spans. The relative Mach number contour of 95% Span presents that after the suction surface synthetic jet excitation, the tip blockage is similar to that of the prototype compressor, so the root cause of compressor stall does not change after the suction surface synthetic jet excitation. At the same time, it can also be obtained that near 5% Span at the root and 95% Span, the synthetic jet of the suction surface has almost no effect on the separation of the suction surface. However, at the height of the middle range between 30% Span and 70% Span, after the excitation of the synthetic jet, the separation degree of the suction surface is slightly smaller than that of the prototype compressor in the first half stage of blowing and the second half stage of inhaling. Although this change cannot expand the stability margin of the compressor, it is beneficial to reduce the separation loss of the trailing edge of the rotor suction surface and then improve the compressor's diffusing work capacity and aerodynamic efficiency. The reason for the analysis is that during the suction stage of the synthetic jet, due to the fact that the suction direction of the synthetic jet is the same as the separation flow direction on the suction surface, the synthetic jet can suck some of the separated flow into the groove, reducing separation losses. However, due to the hysteresis of the excitation of the synthetic jet, it may still be able to reduce the blowing speed until it reaches its maximum. In the blowing stage, the blowing speed direction of the synthetic jet is opposite to the direction of the separated flow on the suction surface, which will further increase the degree of separation and separation loss on the suction surface. This indicates that for the subsonic axial compressor rotor, the suction effect of the synthesized jet at the suction surface position is more effective in reducing flow losses than the blowing effect. Figure 11: \(Cont.\)  
Figure 12 presents the radial velocity contour of the suction surface of the prototype compressor and the compressor excited by the synthetic jet. Just as the effect of synthetic jet on the separation degree of the trailing edge of the suction surface at different spans, when the synthetic jet is in the suction stage, starting from time T\({}_{5}\), as the suction speed of the synthetic jet gradually increases, the separation of the trailing edge of the suction surface in the middle of the blade decreases, reducing the degree of blockage at this position. Therefore, the radial velocity of the flow at this position is higher than that of the prototype compressor, leading to faster convergence of the flow towards the blade tip. The effect of the synthetic jet continues until the \(T_{2}\) moment of the next synthetic jet cycle. In the blowing stage of the synthetic jet (\(T_{3}\)-\(T_{4}\)), the blowing effect actually increases the separation of the suction surface, which creates greater obstacles to the radial movement of the flow, resulting in a slight decrease in radial velocity. Based on the radial velocity analysis of a synthetic jet cycle, after being excited by the suction surface synthetic jet, more air in the compressor channel flows towards the blade tip, resulting in more severe blockage of the blade tip channel than the prototype compressor. Therefore, the stability margin of the compressor rotor has slightly decreased. Based on the analysis of Figures 11 and 12, although the suction effect of the synthetic jet is more advantageous than the blowing effect in reducing losses, it should also be noted that it also causes a slight decrease in the stability margin of the compressor.