# Control of Flow around an Oscillating Plate for Lift Enhancement by Plasma Actuators
## 3 Comparison of the Visualized and Predicted Flow Fields  
Figure 10 shows the visualized flow by the smoke-wire method and the predicted streamline around the oscillating plate with and without control by the actuator at \(t/T=0.0\), \(0.25\), \(0.50\) and \(0.75\). To discuss the flow fields, a simple grid with the lattice spacing of \(2b\) was set in both the figures of the visualized photograph and the predicted streamline. The actuator was installed only on the top surface and continuously driven in the case with control (\(R=100\%\)).  
Figure 9: Predicted variation of lift coefficient for the control condition of \(t_{0}/T=0.0\) and \(R=50\%\) with the original and finer grids.  
As shown in Figure 10, the flow separation from the upstream edge occurs on the top surface except at \(t/T=0.5\) (top dead center) in the baseline case for both the measured and predicted results. A laminar flow separation bubble is observed at \(t/T=0.0\), where the height of the bubble is \(2.1b\) and \(2.0b\) at the downstream point from the leading edge with distance of \(10b\) for the measured and computational results, respectively. In the visualization experiment, the height of separation bubble was averaged for ten photographs and the variation was about 6%. Also, the height of separation bubble at the above-mentioned point at \(t/T=0.25\) is \(2.6b\) and \(2.4b\) for the measured and computational results, respectively. Also, the flow reattachment occurs at the above-mentioned point at \(t/T=0.75\) for both the measured and predicted results. These results present that the predicted flow fields at each time are in agreement with those visualized for the baseline case. In the case with control, the flow separation around the leading edge is almost suppressed, while the flow is slightly separated around the center of the plate, particularly at \(t/T=0.25\). These flow behaviors were observed in both the measured and predicted flow fields.  
In the previous paper from the same group [31], the predicted control effects on the flow around a fixed plate (\(\alpha=0^{\circ}\)) by the plasma actuator were compared with those measured by a hot-wire anemometer. In this study, the actuator with the same configurations as that in the present paper was located at the same position with the distance of \(0.25b\) from the leading edge. The computational model of the body force by the actuator was also the same as that in the present computations. Figure 11 shows the predicted and measured vertical distributions of the mean velocity and turbulence intensity with and without the control by the actuator at the downstream position from the leading edge with the distance of \(4.5b\). Both the predicted and measured results show the suppression of the flow  
Figure 10: The visualized flow pattern and predicted streamlines (upper right in each figure) around the oscillating plate with and without control by the actuator on the top surface (\(R=100\%\)), where \(T\) is an oscillation period and \(t=0\) represents the time for the bottom dead center of the oscillating motion.  
separation by the control [31]. Also, both the predicted distributions with and without control are in good agreement with those measured.  
These results suggest that the present computations correctly capture the flow fields around the oscillating plate, including the control effects of the plasma actuator.