# Influence of Active Flow Control of Synthetic Jet at
## 5 Influence and Analysis of Synthetic Jet on Compressor Performance
### Internal Flow Analysis of Compressor
Figure 11: Relative Mach number contour at different spans. Figure 13 presents the limiting streamlines of the suction surface of the prototype compressor and the compressor excited by the synthetic jet. At \(T_{1}\), due to the influence of the suction effect of the previous synthetic jet cycle, at this time, the separation line at the trailing edge of the suction surface almost coincides with the jet slit, and a second separation line appears near the trailing edge of the blade after the separation line, and a separation bubble is formed between the two separation lines. With the increase in blowing velocity, the blowing effect of the synthetic jet will blow the flow behind the jet slit downstream, the separation bubble and the second separation line disappear, and the first separation line also moves upstream of the jet slit. The forward movement of the separation line indicates that the separation degree of the trailing edge of the suction surface increases, resulting in a corresponding increase in separation loss. From the figure, it can also be seen that as the blowing speed of the synthetic jet increases, it actually hinders the upward movement of the radial flow and alleviates the blockage at the blade tip. But soon after \(T_{5}\), the blowing velocity drops to 0, and the synthetic jet is about to enter the suction phase. With the increase in the suction velocity, the synthetic jet will suck the low-speed flow behind the separation line into the slit, making the original separation line of the suction surface gradually move towards the trailing edge of the blade. When it moves back to the slit, it will stop moving back and stabilize at this position, so the suction surface will move back. It indicates that the separation of the trailing edge of the suction surface is reduced, and the separation loss of the compressor is also reduced. In the suction stage, due to the absorption of the separated flow at the trailing edge of the suction surface by the synthetic jet, the radial flow accelerates the convergence towards the blade tip, resulting in a decrease in compressor margin. At the same time, downstream of the jet slit, due to the synthetic jet not completely absorbing the flow before the slit, there is still a very small portion of the flow that crosses the jet slit and moves downstream. This portion of the flow separates from the original suction surface trailing edge and converges at the downstream position of the jet slit, gradually forming a second separation line at that position. Therefore, separation bubbles appear between the two separation lines. Due to the hysteresis of the compressor response after the synthetic jet excitation, as the suction speed increases, the second separation line continues to move downstream, and the axial range of the separation bubble expands. This process continues until the suction speed reaches its maximum \(T_{7}\) moment and is still reflected at the \(T_{1}\) moment when the blowing begins in the next synthetic jet cycle. Figure 12: Contour of radial velocity. Figure 14 presents the variation of the relative total pressure loss coefficient of the measured section at the compressor outlet during a synthetic jet cycle. The total pressure loss coefficient of the compressor presents a standard sinusoidal law, but its phase lags the inlet velocity of the synthetic jet by about \(1/8\ T\). At the same time, at the beginning of the synthetic jet blowing stage and the whole suction stage, the total pressure loss coefficient is lower than that of the prototype compressor, and the maximum loss coefficient is reduced by 45.85%, with an average reduction of 8.61%, which indicates that for the synthetic jet excitation on the suction surface, the suction effect is more favorable than the blowing effect for reducing the compressor loss. In order to more carefully observe and compare the changes in compressor losses before and after the synthetic jet excitation on the suction surface, the loss source is used to quantify the description method.