# Effect of NS-DBD Actuator Parameters on the Aerodynamic Performance of a Flap Lifting Device
## 4 Simulation Results and Analysis
### Comparisons of Discharge Frequency
#### 4.1.1 Comparison Results of the Aerodynamic Forces and Moments  
(1) Drag Coefficient  
The control effects of the three selected discharge positions are not obviously different in the drag coefficient. Compared with the specific decrease value and the drag curve trend, it can be found that the lower trailing edge position has a better drag reduction effect, but increasing the discharge frequency will weaken the drag reduction effect, especially when the flow field has been obviously separated but not completely stalled at 8 and 10\({}^{\circ}\) angles of attack, and the reduction of drag generated by a 200 Hz discharge frequency is significantly lower than that generated by 100 Hz. The upper trailing edge discharge position leads to the increase of drag, the increase in frequency will strengthen this adverse effect, which makes the drag obviously greater than that without the discharge, and it is more likely for this trend to form in the case of large area of the separation flow. For the upper surface discharge position, the change of discharge frequency has no obvious influence on the drag coefficient, as shown in Figure 4.  
It can be inferred that the increase of discharge frequency improves the incentive efficiency to some extent, that is, the flow field under high-frequency excitation can be stabilized in a shorter period of time. However, there is no obvious advantage in the reduction of airfoil drag.  
(2) Lift Coefficient  
In terms of lift coefficient, the effect of the 200 Hz discharge frequency is different from that of 100 Hz at different positions: Weakening at the lower trailing edge, strengthening at the upper trailing edge, and no obvious effect at the upper surface. For the lower trailing edge discharge, when the frequency increases, the lift coefficient does not increase, and instead is actually slightly weakened, and the increment rate decreases with different degrees in the full range of angle of attack. For the upper trailing edge discharge, the increase in frequency can significantly increase the lift increment. For example, when the flow field at a 12\({}^{\circ}\) angle of attack has been separated, the lift increment can be increased from 12.85% to 15.8%. For the upper surface discharge, there is no obvious difference at the two discharge frequencies, as shown in Figure 5.  
It can be inferred that, for the lower trailing edge discharge with a relatively limited effect of flow field range, increasing the frequency will not increase the lift, and even the effect of the flow field will decrease because the pulses pass through the gap (between the main wing and flap) too quickly. For the upper trailing discharge with large effect range and higher lift increment, the increase in frequency can strengthen this trend, which can result in quicker vortex shedding of the upper surface of the flap and more efficient effect of the pulse wave.  
Figure 4: The drag coefficient curve at different discharge frequencies.  
(3) Lift-Drag Ratio  
The three different discharge positions all show a law that the lift-drag ratio decreases as the discharge frequency increases, as shown in Figure 6. At the upper trailing edge position, there is little contribution to the lift-drag ratio near an 8\({}^{\circ}\) angle of attack at a 200 Hz discharge frequency.  
Figure 5: The lift coefficient curve at different discharge frequencies.  
Figure 6: Cont.