5. Study on effects of flow control parameters
Although synthetic jet control has been proven to be able to effectively restrain flow separation, the control effects greatly de-pend on the selection of flow control parameters. Therefore, it is necessary to analyze the role of typical flow control parameters on control efficiency.
5.1. Influence of jet location
The study of jet locations mainly analyzes the effect of the in-stallation location of the jet actuators on the flow characteristics. Two types of actuator layout at the leading edge and 1%cof the upper surface for the model are selected. The jet parameters for each actuator are set at cμ=0.00408%, F+=1.0583, and the jet deflection angle is set at θjet=90◦, i.e. normal fluidic control is adopted.
Fig.11shows a comparison of the model aerodynamic charac-teristics before and after flow control. It can be seen that when the angle of attack is less than 10◦, there is almost no impact from the flow control as the model flow is still attached.
As the angle of attack increases, the wing upper surface of the model starts experiencing flow separation and flow control be-comes active. However, the difference is that actuators (R11–R14) suppress the separation of flow and improve the aerodynamic characteristics of the model, while actuators (R21–R24) amplify the separation of flow and cause further deterioration of the aerody-namic characteristics of the model.
Fig.12shows a comparison of the time-averaged pressure co-efficient distribution of the model at typical spanwise stations under different actuator layouts when α=12◦. It is found that (R21–R24) have little impact on the main flow field and these ac-tuators cause only a weak local pressure jump. The flow field at this location shows a complete separation and the jet disturbance will be quickly distinguished, producing insufficient impact on the main flow field. Actuators (R11–R14) cause obvious suppression of the separated flow, because the jet actuators are located in a sensi-tive area of the leading edge and the jet disturbance and main flow interfere with each other. This greatly improves the negative pres-sure value of the wing upper surface of the model, and reduces the flow separation of the wing surface, thus enhancing the lift performance of the aircraft. As the negative pressure increment is relatively concentrated on the outer wing surface, the pitch down moment of the model is enhanced. In addition, the jet disturbance also propagates over a long distance in the downstream direction, producing a beneficial effect on whole chordwise flow, although gradually weakening the disturbance intensity.
It can be seen that the installation position of the actuators greatly influences the flow control effect. If an appropriate posi-tion is selected, the actuator disturbance can be transmitted over a long distance, producing an obvious influence on the main flow field. An inappropriate layout of the actuators may only produce disturbance of the local flow field near to the installation position, producing an insufficient macro-impact on the main flow field.