# Influence of Active Flow Control of Synthetic Jet at
## 4 Synthetic Jet Design  
To investigate the synthetic jet on the suction surface of rotor blade, it is necessary to determine the excitation position. What can be learned from the existing research is that when the boundary layer of the suction surface of the compressor rotor blade is pumped, the suction position is usually arranged in the separation zone rather than in front of the separation zone. This is because the main purpose of boundary layer suction is to extract the low-energy fluid on the blade surface to weaken the separation of the suction surface. If the suction position is arranged in front of the separation area, it is bound to suck the non-separated flow early but cannot inhibit the separated gas flow. However, it should be noted that the suction position should not be arranged too far back in the separation area. At this time, the flow has been greatly separated, and suction at the too-far back position will affect the suction mass flow and effect. Therefore, when performing boundary layer suction, the suction position is usually arranged in the first half of the separation zone. Using the method of boundary layer suction for reference, the excitation position is also arranged in the separation zone when the synthetic jet on the suction surface of the rotor blade is investigated. In fact, because the total pressure ratio of this subsonic compressor rotor is low, the separation line of the suction surface is close to the trailing edge of the blade, and the thickness of the trailing edge blade is limited, it is not suitable to set multiple synthetic jet excitation slots to investigate the optimal axial position of the excitation. Therefore, this paper only designs and calculates one excitation position. As depicted in Figure 8, the axial position of synthetic jet excitation is 88% Ca from the leading edge (Ca refers to the axial chord length of the blade tip). To prevent the interference of clearance flow, 1 mm is reserved from the synthetic jet to the blade tip. In the numerical simulation, the outlet velocity model is adopted. The grid on one side of the suction surface of the rotor blade is locally densified, and 0.3 mm wide is cut out as the velocity outlet of the synthetic jet. The boundary condition of the velocity inlet is directly given at the outlet, and the angle between the jet direction and the tangent direction of the suction surface is about 30\({}^{\circ}\). The velocity of the synthetic jet is defined as follows:  
\[V(t)=V_{\text{max}}\sin(2\pi ft+\varphi) \tag{3}\]  
In the above equation, the initial phase \(\varphi\) is set to 0. The selection of other parameters is based on reference [14], which also conducted numerical simulation research on the synthetic jet on the suction surface of an axial compressor rotor. The excitation frequency in the paper is 600 Hz, and the jet peak velocities are 200 m/s and 300 m/s, respectively. For the setting of jet peak velocity, the paper points out that the actual synthetic jet actuator can reach a value of 80-120 m/s, but the value used in reference [14] far exceeds the maximum value generated by the actual synthetic jet actuator. However, the author further emphasizes that their purpose is not to provide strict real-world figures but to demonstrate how high the jet velocity should be to have an undeniable impact on transonic blades. Figure 7: Proportion of loss sources in compressor rotor. As the research object of this paper is a subsonic compressor, the jet peak velocity can be further reduced. Therefore, referring to the parameter settings in reference [14], this paper sets the excitation frequency and jet peak velocity as \(f\) = 600 Hz, _Vmax_ = 50 m/s. The velocity distribution of a sinusoidal form of synthetic jet in a period is depicted in Figure 9. Eight typical moments are also highlighted. In the unsteady calculation of simulating synthetic jet excitation, the time term adopts the second-order backward Euler scheme, the physical time step is 1/20 of a synthetic jet cycle, and each physical time step has 10 virtual time steps.