# Experimental Study on Anti-Icing Performance of NS-DBD Plasma Actuator
## 3 Experimental Results
### Anti-Icing Performance  
Anti-icing experiments using a NS-DBD plasma actuator with two different discharge conditions were conducted under the conditions of U = 65 m/s, T = \(-10\)\({}^{\circ}\)C, LWC = 0.5 g/m\({}^{3}\), MVD = 25 \(\upmu\)m. The experiment was conducted as follows. Firstly, the wind tunnel was adjusted to the target parameters for at least an hour in order to reach a steady state. The plasma actuator was then then switched on for about 100 s to attain thermal equilibrium. Here, the moment switch on the plasma actuator is set as t = 0 s. When t = 100 s, the spray system was opened. Figure 13 shows the dynamic anti-icing process of two different discharge conditions. As time goes on, the supercooled water droplets continuously impinge on the front part of airfoil model. Figure 11: The surface temperature distribution 80 s after NS-DBD plasma actuator was switched on under the condition of U = 65 m/s, T = \(-10\)\({}^{\circ}\)C, LWC = 0 g/m\({}^{3}\): (**a**) LV-HF discharge; (**b**) HV-LF discharge. Figure 12: The spanwise (direction of X axis) temperature variation of Y = 10 mm, Y = 20 mm, Y = 30 mm: (**a**) LV-HF discharge; (**b**) HV-LF discharge. When applied with HV-LF discharge, as Figure 13a shows, the supercooled water droplets hitting the discharge region are melted and run backwards. In contrast, on the other front part of the airfoil model (with no protection), ice accumulation occurs. In the case of HV-LF discharge, the appearance of ice accumulation on the airfoil surface changes to a great extent. During the discharge region, ice accretion firstly occurs between two adjacent electrodes at the leading edge of the airfoil, as shown in Figure 13b, when t = 150 s. Then, the ice area is gradually enlarged until it covers the whole leading edge. The discharge occured beneath the ice layer, as shown in Figure 13b when t = 250 s. It was not enough to melt the ice crust above, due to only a thin layer of heated air (less than 1 mm as reported in reference [21; 24]) being formed. In summary, with the same total power input, the LV-HF discharge of NS-DBD plasma actuator has a better anti-icing performance than the HV-LF discharge. To further explore the reasons for this, the surface temperature distribution during the anti-icing process was used for analysis. Figure 14 shows the time variation of the surface temperature distribution measured by thermal infrared imager (FLIR) during the anti-icing process, when applied with LV-HF discharge (\(V_{p\text{-}p}\) = 8.6 kV, \(f_{p}\) = 6 kHz). It can be clearly seen that the impingement of supercooled water droplet results in a cooling of the dielectric surface. Supercooled water droplets  
Figure 13: Dynamic anti-icing process of NS-DBD plasma actuator: (**a**) LV-HF discharge; (**b**) HV-LF discharge. are heated up and form a thin water film which runs backwards and develops into isolated water rivulets. The surface temperature of the water film and rivulets downstream from the heating zone kept decreasing in the backward process, which led to the heat transfer with the airfoil surface and surrounding airflow. Figure 15 shows the time variation of the surface temperature distribution when applied with HV-LF discharge (\(V_{p,p}=13.6\) kV, \(f_{p}=2\) kHz), under the same icing conditions. It can be observed that the surface temperature significantly drops after opening the spray system. When t = 150 s (50 s after opening the spray system), the temperature located at the middle of two adjacent exposed electrodes has already dropped below zero, which means that it has already frozen there. The ice surface subsequently extends. When t = 200 s, part of the surface has reached a temperature equal to that of the cold airflow (\(-10\)\({}^{\circ}\)C). To further evaluate the surface temperature variation during anti-icing process, three points A, B, and C (as Figure 8 shows) were selected. Figure 16 plots the time variations of surface temperature at the location of selected points.