Table of Contents
Plasma flow control, based on the plasma aerodynamic actuation, is a novel active flow control technique to improve aircrafts’ aerodynamic characteristics and propulsion efficiency. Plasma flows control has drawn considerable attention and been used in boundary layer acceleration, airfoil separation control, forebody separation control, turbine blade separation control, axial compressor stability extension, heat transfer and high-speed jet control. Plasma aerodynamic actuator has many advantageous features including robustness, simplicity, low power consumption and the ability for real-time control at high frequency. 1
The principle of plasma aerodynamic actuation and its application in subsonic and supersonic flow control was summarized. To better understand the underlying physical mechanism of plasma flow control and optimize the geometric configuration of the actuator, the characteristics of the plasma aerodynamic actuation, including gas temperature, electron density and temperature, induced body force, velocity and vorticity were investigated. Both wind tunnel experiments and computations were performed to investigate the flow control capability of plasma aerodynamic actuation for airfoil separation control, corner separation control, axial compressor stability extension and shock wave control.2
Plasma Aerodynamic Actuation:
The mechanism for plasma flow control can be summarized as a momentum effect, shock effect, and chemical effect. Momentum effect induces near-surface flow velocity of 1-6 m/s. Shock effect induces local gas pressure or temperature rise near the electrode. The chemical effect adds new particles, such as ions, electrons, and excited particles, into the flow field. Surface dielectric barrier discharge plasma aerodynamic actuation is typically used in the subsonic plasma flow control, while arc discharge plasma aerodynamic actuation is mostly used in the supersonic and hypersonic plasma flow control. Plasma aerodynamic actuation generated by corona discharge, radiofrequency discharge, microwave discharge is also widely investigated.3
Surface dielectric barrier discharge plasma aerodynamic actuation:
A schematic of the dielectric barrier discharge plasma aerodynamic actuator is shown in the figure. Most of the previous experimental and simulation studies mainly focused on the asymmetric dielectric barrier discharge plasma aerodynamic actuation excited by sinusoidal or sawtooth voltage waveforms at an amplitude of 2-20 kV and frequency of 1-100 kHz, which can be named as the microsecond discharge plasma aerodynamic actuation. In recent years, the plasma aerodynamic actuation generated by nanosecond pulsed dielectric barrier discharge has become a hot topic.
Synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation were performed. Fig. 1 shows the schematic diagram of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuator. The dielectric layer used is a RO4350B (Rogers Corporation) plate with a relative permittivity constant of 3.48. The electrodes are made of copper, covered with a thin layer of lead-tin film. The plasma aerodynamic actuator is driven by a high-frequency high voltage power supply (CTP-2000K, Suman Electronics). The output voltage range and frequency range of the power supply are 0~40 kV and 6~40 kHz respectively.
The experimental arrangement is shown in Fig. 2. Synthetic measurements are applied to measure both the plasma and the induced flow characteristics of the plasma aerodynamic actuation. The applied voltage and the total discharge current are measured by a high voltage probe (P6015A, Tektronix Inc.) and a current probe (TCP312+TCPA300, Tektronix Inc.). Signals are recorded on an oscilloscope (DPO4104, Tektronix Inc.). Optical emission spectroscopy is measured by a 0.5m monochrometer (TRIAX550, Jobin Yvon Inc.) through an optical fiber collector, 1 cm over the surface of the dielectric layer. 4
The detector of the monochrometer is a set of photon counting system (Model 76915, Oriel Inc.). The slit width and the calibrated resolution, in this case, are 20μm and 0.05nm. The emission intensity is averaged temporally and spatially. Body force induced by the plasma aerodynamic actuation is measured by an electronic balance(ABS 204-S, Mettler Toledo Inc.). Velocity and vorticity induced by the plasma aerodynamic actuation are measured by Particle Image Velocimetry (Lavision). The air is seeded by vaporization of mineral oil with a mean size of about 0.3 μm.
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