Flow separation control by plasma actuator with nanosecond pulse periodic discharge

Abstract

Currently, the problem of flow active control by low-temperature plasma is considered to be one of the most booming realms of aerodynamics . The paper presents a results on controlling boundary layer attachment by plasma actuator withhighvoltage pulsed periodic nanosecond excitation. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region at fast (τ ≃ 1μs) thermalization of the plasma inputed energy. The mean values of such heating of the plasma layer can reach 70, 200, and even 400 K for 7-, 12-, and 50-ns pulse durations, respectively. The emerging shock wave together with the secondary vortex flows disturbs the main flow. The resulting pulsed-periodic disturbance causes an efficient transversal momentum transfer into the boundary layer and further flow attachment to the airfoil surface. Thus, for periodic pulsed nanosecond dielectric barrier discharge DBD, the main mechanism of impact is the energy transfer to and heating of the near-surface gas layer. The following pulse-periodic vortex movement stimulates redistribution of the main flow momentum. The experiments performed here have shown high efficiency of the given mechanism to control boundary layer separation, lift and drag force coefficients, and acoustic noise reduction in the Mach number range of 0.05 to 0.85. The design of the SDBD was typical asymmetric plasma actuator with one exposed and one covered electrodes . In our experiments, the exposed electrode was a cathode. The lower covered electrode was an anode. The experiments were carried out on the generator with a pulse length of 12 ns. Two regimes of the generator's operation were used. One was periodic, with a constant frequency of pulses fed onto the discharge gap. The other was burst mode, with impulses fed in bursts. The number of pulses in a burst varied from 1 to 100 with a repetition frequency of 100 kHz, and the time between the bursts being 1-100 ms. The number of pulses in the burst varied to produce constant averaged discharge power for various experimental conditions. The mean power in all burst regimes was equal to 25 W.The electrodes were made of 50 ?m aluminum foil. Their length was 90 cm and their widths were 15 and 10 mm for the lower and upper electrodes, respectively. The dielectric layer consisted of three PVC-films with a total thickness of 240 ?m.