No abstract

Plasma flow control (PFC) is a promising active flow control method with its unique advantages including the absence of moving components, fast response, easy implementation, and stable operation. The effectiveness of plasma flow control by microsecond dielectric barrier discharge (µs-DBD), and by nanosecond dielectric barrier discharge (NS-DBD) are compared through the wind tunnel tests, showing a similar performance between µs-DBD and NS-DBD. Furthermore, the µs-DBD is implemented on an unmanned aerial vehicle (UAV), which is a scaled model of a newly developed amphibious plane. The wingspan of the model is 2.87m, and the airspeed is no less than 30m/s. The flight data, static pressure data, and Tufts images are recorded and analyzed in detail. Results of the flight test show that the µs-DBD works well on board without affecting the normal operation of the UAV model. When the actuators are turned on, the stall angle and maximum lift coefficient can be improved by 1.3 • and 10.4%, and the static pressure at the leading edge of the wing can be reduced effectively in a proper range of angle of attack, which shows the ability of µs-DBD to act as plasma slats. The rolling moment produced by left-side µs-DBD actuation is greater than that produced by the maximum deflection of ailerons, which indicates the potential of µs-DBD to act as plasma ailerons. The results verify the feasibility and efficacy of µs-DBD plasma flow control in a real flight and lay the foundation for the full-sized airplane application.

Surface dielectric barrier discharge (SDBD) actuators driven by the pulsed-DC voltages are analyzed. The pulsed-DC SDBD studied in this work is equivalent to a classical SDBD driven by a tailored fast-rise–slow-decay (FRSD) voltage waveform. The plasma channel formation and charge production process in the voltage rising stage are studied at different slopes using a classical 2D fluid model, the thrust generated in the voltage decaying stage is studied based on an analytical approach taking 2D model results as the input. A thrust pulse is generated in the trailing edge of the voltage waveform and reaches maximum when the voltage decreases by approximately the value of cathode voltage fall (≈ 600 V). The time duration of the rising and trailing edge, the decay rate and the amplitude of applied voltage are the main factors affecting the performance of the actuator. Analytical expressions are formulated for the value and time moment of peak thrust, the upper limit of thrust is also estimated. Higher voltage rising rate leads to higher charge density in the voltage rising stage thus higher thrust. Shorter voltage trailing edge, in general, results in higher value and earlier appearance of the peak thrust. The detailed profile of the trailing edge also affects the performance. Results in this work allow us to flexibly design the FRSD waveforms for an SDBD actuator according to the requirements of active flow control in different application conditions.

Dielectric barrier discharge using pulsed-DC high voltage (pulsed-DC DBD) have been proven to be capable of effectively reducing skin friction drag in turbulent boundary layers with limited power consumption, thus producing significant net power savings. In this work, the characteristics of pulsed-DC DBD, including power consumption, induced flow structure, thermal effect, and body force, are investigated sequentially. Both the power consumption and pressure waves produced by pulsed-DC DBD are similar to that of DBD using nanosecond pulses (ns-DBD), whereas the wall-bounded jet structure resembles that of DBD using sinusoidal high voltage (ac-DBD). A curved wall jet is induced at a small pulse width, which turns into a straight one due to the combined effect of momentum and thermal addition when the pulse width increases. With increasing pulse width, the induced body force goes up while the thermal effect weakens. Although pulse frequency has no impact on the wall-bounded jet topology, the body force increases with pulse frequency because of the enhanced energy entrainment. With these results, four parameters that affect the performance of pulsed-DC DBD are extracted, including the pulse leading edge, pulse width, frequency, and amplitude, which lays the foundation for the optimization of pulsed-DC DBD.

In this study, high-voltage pulses are used to drive dielectric barrier discharge plasma actuators (DBDAs) for flow control purposes. The rising/falling edges of the pulse are kept nearly constant in nanosecond timescale, while the pulse width is varied from nanosecond to microsecond timescale. The impact of pulse width on the characteristics of the DBDA is investigated experimentally with a high-speed schlieren system and a high-fidelity force balance. In the case of small pulse width, a pressure wave propagating at the local speed of sound is produced each time at discharge ignition, and a vertical jet plume is induced after multiple discharge pulses due to heat accumulation (buoyancy effect). As a comparison, for cases with large pulse widths, two pressure waves are created sequentially with a time lag close to the pulse width, and a starting vortex followed by a near-wall jet is produced, demonstrating that significant momentum similar to that of DBD driven by sinusoidal high voltage has been imparted to the near-wall flow. A proportional increase of the induced body force with the cube root of the pulse width is demonstrated, while the pulse energy decreases nonlinearly as the pulse width increases. The maximum body force of 2.49 mN m−1 is reached at a pulse width of 380 μs.