Nanosecond-Pulsed Discharges for Plasma-Assisted Combustion and Aerodynamics

The efficiency of nanosecond discharges as an active-particle generator for plasma-assisted combustion and ignition has been shown. The kinetics of alkane oxidation have been investigated from methane to decane in stoichiometric and lean mixtures with oxygen and air at room temperature under the action of high-voltage nanosecond unform discharge. The study of nanosecond barrier discharge influence on a flame propagation and flame blowoff velocity has been carried out. A significant increase of the flame blowoff velocity has been demonstrated. A decrease of 2-3 orders of magnitude of the plasma-assisted ignition delay time in comparison with the autoignition has been registered. Detonation initiating by high-voltage gas discharge has been demonstrated. The energy deposition in the discharge ranging from 70 mJ to 12 J for propane-oxygen-nitrogen mixtures leads to the transition to detonation at a distance of less than one diameter of the detonation tube. The influence of pulsed surface dielectric discharge on the flow separation for airfoils at a high angle of attack has been investigated within the velocity range from 20 to 110 m/s for the power consumption less than 1 W/cm of the wing span. The conclusion has been made that the main mechanism of plasma impact is the boundary-layer turbulization rather than acceleration

Flow Separation Control on Airfoil With Pulsed Nanosecond Discharge Actuator

An experimental study of flow separation control with a nanosecond pulse plasma actuator was performed in wind-tunnel experiments. The discharge used had a pulse width of 12 ns and rising time of 3 ns with voltage up to 12 kV. Repetition frequency was adjustable up to 10 kHz. The first series of experiments was to measure integral effects of the actuator on lift and drag. Three different airfoil models were used, NACA-0015 with the chord of 20 cm, NLF-MOD22A with the chord of 60 cm and NACA 63-618 with the chord of 20 cm. Different geometries of the actuator were tested at flow speeds up to 80 m/s. In stall conditions the significant lift increase up to 20% accompanied by drag reduction (up to 3 times) was observed. The critical angle of attack shifted up to 5–7 degrees. The relation of the optimal discharge frequency to the chord length and flow velocity was proven. The dependence of the effect on the position of the actuator on the wing was studied, showing that the most effective position of the actuator is on the leading edge in case of leading edge separation. In order to study the mechanism of the nanosecond plasma actuation experiments using schlieren imaging were carried out. It shown the shock wave propagation and formation of large-scale vortex structure in the separation zone, which led to separation elimination. PIV diagnostics technique was used to investigate velocity field and quantitative properties of vortex formation. In flat-plate still air experiments small scale actuator effects were investigated. Measured speed of flow generated by actuator was found to be of order of 0.1 m/s and a span-wise nonuniformity was observed. The experimental work is supported by numerical simulations of the phenomena. The formation of vortex similar to that observed in experiments was simulated in the case of laminar leading edge separation. Model simulations of free shear layer shown intensification of shear layer instabilities due to shock wave to shear layer interaction.Aerodynamics, Wind Energy & PropulsionAerospace Engineerin

Spontaneous Raman scattering: a useful tool for investigating the afterglow of nanosecond scale discharges in air

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