# Effect of NS-DBD Actuator Parameters on the Aerodynamic Performance of a Flap Lifting Device
## 4 Simulation Results and Analysis
### Comparisons of Discharge Pulse Width
#### 4.2.2 Comparative Analysis of the Flow Field Structure  
Similarly, the flow field structure with a 12\({}^{\circ}\) angle of attack is selected. Four different moments of a single pulse are taken to analyse the effect differences at different moments. From the velocity distribution diagram (Figure 13), when the pulse width increases, the actual discharge time in a period increases, and the disturbance in the flow field also lasts longer, which will produce more obvious pulse waves. When the plasma actuator is applied to the lower surface of the main wing close to the trailing edge, the disturbance generated by the discharge will first interfere with the flow in the gap between the main wing and flap and then propagate forward and backward at the same time after  
Figure 11: Lift coefficient curve of variable pulse width.  
Figure 12: Lift-drag ratio coefficient curve of variable pulse width.  
acting on the upper surface of the flap. The backward disturbance can effectively accelerate the flow on the upper surface of the flap, while the forward disturbance is contrary to the original flow direction, which does not help to reduce the drag. When the pulse width is small (50 and 200 ns), the forward pulse is quickly consumed, and the backward pulse reduces the low-speed zone on the upper surface of the flap and the trailing edge. When the pulse width is large (500 ns), the effect of discharge on the separated area is slightly better than that under the condition of small pulse width. However, when part of the energy flows to the upper and lower surface of the main wing, an arc-shaped wave with a large velocity gradient will be generated and advance to the leading-edge point, which is unfavourable. The pulse width of 200 ns obviously accelerates and integrates the separation flow in the low-speed zone, and it is not sufficiently strong to interfere the airflow above and below the main wing; therefore, the front and rear flow fields are well balanced, and relatively better the lift-drag ratio is obtained.  
As seen from the vorticity distribution diagram (Figure 14), the increased pulse width can cause stronger vortex shedding and have a more obvious reduction effect on the large vorticity area on the upper surface of the flap. However, the upper and lower flow fields of the main wing are also more affected.  
Figure 13: The velocity distribution under single pulse discharges with different pulse widths.  
In terms of the vorticity of the concave zone in the lower gap of the main wing, the discharges with 50 and 100 ns pulse widths have appropriate perturbation effects on it, and in the process of the excitation spreading, the vorticity can be reduced obviously. The discharge with the 500 ns pulse width first completely breaks the vorticity here and then continues to spread forward, resulting in a strong vortex in the gap between the main wing and flap, which has an adverse effect on the flow.  
From the pressure distribution diagram (Figure 15), the annular high-pressure area formed by the large pulse width discharge even has a multi-layer high-pressure area, and the duration is longer. Pressure fluctuations can also affect a wider range, extending to the upper and lower surfaces of the entire airfoil. When the pressure wave is about to dissipate, the disturbance effects of different pulse width discharges on the lower surface of the airfoil are similar. In the process of the propagation of the discharge pulses with 200 and 500 ns pulse widths, the high-pressure parts last too long, resulting in a very strong disturbance of the upper and lower flow field and have no obvious advantage in the pressure difference. It is not better than the small pulse width discharge in the increasement of lift.  
Figure 14: The vorticity distribution under single pulse discharges with different pulse widths.