**2. Experimental Setup**

The experiment was carried out in Harbin AVIC Aerodynaiviics Research Institute, and two wind tunnels were selected for experiments. The wind tunnel in Figure 1 is FL-5, which was an open low-speed wind tunnel with an experimental section size of 1.5 m × 1.95 m (diameter × length), a maximum wind speed of 53 m/s, and a turbulence intensity of 1%. Figure 2 shows the FL-51 wind tunnel, which is a single-loop continuous wind tunnel with replaceable open/closed ports. The test section was 11 m × 4.5 m × 3.5 m (length × width × height), and the maximum airflow velocity of the closed experimental section was 100 m/s; the turbulence intensity was 0.10%.

**Figure 1.** FL-5 wind tunnel open test section.

**Figure 2.** FL-51 wind tunnel closed test section.

The two kinds of scaling flying wing models are shown in Figures 3 and 4. The small flying wing was double "W" shape, the leading edge sweep angle was 35◦, the spanwise length was 0.953 m, the fuselage length was 0.386 m, and the average aerodynamic chord length was 0.214 m. The geometric parameters of the large flying wing were 2.5 times those of the small flying wing.

**Figure 3.** Small flying wing model.

**Figure 4.** Large flying wing model.

An adjustable parameter microsecond pulse power supply was used for the power supply of the plasma actuator. The schematic circuit diagram is shown in Figure 5. The input AC voltage was between 0–220 V, and a relatively stable DC voltage was obtained through the full bridge rectifier (BR) and the voltage regulator capacitor *C1*. Then, it charged the primary energy storage capacitor *C2* through the charging inductor *L* and the diode *D1*. The voltage of the primary storage capacitor *C2* was about 1.4 times of the input voltage by *C1*. When the semiconductor switching insulated gate bipolar transistor (IGBT) was working, *C2* performs pulse discharge. A positive high voltage pulse was generated by potential transformer (PT) boost and diode *D3* unidirectional conduction. The output actuation voltage (peak voltage) was adjustable from 0 to 10 kV, and the pulse frequency was adjustable from 0 to 2 kHz. The waveform of the no-load maximum output voltage is shown in Figure 6. Each single pulse duration time was microsecond magnitude. When the circuit exported a high-voltage pulse, the actuator performed a single pulse discharge. The number of high-voltage pulses produced in a second was the pulse repetition frequency.

**Figure 5.** Microsecond pulse power supply schematic circuit diagram.

**Figure 6.** Waveform of no-load maximum output voltage (*U*).

The actuator in the experiment was composed of exposed electrode, covered electrode, and insulation dielectric, as shown in Figure 7. The covered electrode was 3 mm wide and 0.06 mm thick and its lower edge was aligned with the leading edge of the flying wing. The exposed electrode was 2 mm wide and 0.06 mm thick and the upper edge was aligned with the leading edge of the symmetric flying wing. The insulation dielectric was made of polyimide, with a thickness of 0.18 mm, a dielectric constant of 3.5, and could withstand a high voltage of 15 kV. It was placed between the two electrodes to separate them.

**Figure 7.** Surface dielectric barrier discharge actuator. (**a**): structure; (**b**): position layout.

The experiment used the PIV velocity measurement system to measure the flow field parameters by the non-contact method and study the characteristics of the plasma actuation inducing flow field. Figure 8 shows the placement of the PIV test system. The laser was an integrated double Nd:YAG laser with a single pulse energy of up to 500 mJ and a wavelength of 532 nm. The CCD camera has a pixel resolution of 16 MP (4904 × 3280 pixels), a grayscale resolution of 12 bits, and an image acquisition frequency of 3.2 fps. The system was synchronized using a programmable time controller (PTU) with a control signal time resolution of 0.3 ns. PIV data acquisition and processing were carried out by Davis 8.3 software. The tracer particles were produced by pressure atomization. The particle medium was olive oil, and the tracer particles were about 1 μm in diameter. In the time scale of microseconds, two images were taken in succession. The images captured the oil mist particles applied to the flow field. The position of the particles in the second image was obtained by image correlation theory, so as to calculate the velocity of particles in the flow field by the position of particles in two images.

**Figure 8.** Particle image velocimetry (PIV) test system layout diagram.

The wind tunnel force measurement was measured by a rod-type strain balance, and the model was supported by a single-strut. The test photographs are shown as Figures 3 and 4. The rod-type six-component strain balance was installed inside the model, and the model is connected with the abdominal support rod through a balance. VXI (VMEbus Extension for Instrumentation) data acquisition system was used for balance force data acquisition.

The small and the large flying wings were tested in two di fferent size wind tunnels, FL-5 and FL-51, respectively. The wind speed of FL-5 was a constant 30 m/s. The wind speed of FL-51 was a constant 75 m/s. The test conditions are shown in Table 1.


**Table 1.** The test conditions.
