Flow Separation Control on Airfoil With Pulsed Nanosecond Discharge Actuator

Abstract

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.

Dynamics of Rapid Localized Heating in Nanosecond Pulse Discharges for High Speed Flow Control

“…In other words, flow forcing in LAFPA and nanosecond pulse DBD actuators may well occur on the same time scale, and the mechanisms of flow control for both types of actuators may be similar. Indeed, large-scale structures (spanwise vortices) detected in recent studies of high-speed airfoil flow control using nanosecond pulse DBD plasma actuators [11][12][13][14] are similar to those detected in experiments using LAFPA actuators in jet flows.…”

“…2). This effect results in flow reattachment over a wide range of discharge pulse repetition rates [11][12][13][14]. Also, compression waves generated in a NS-DBD actuator placed on the surface of a cylinder model in a Mach 5 flow were demonstrated to strongly perturb the bow shock in front of the model, which increased the shock stand-off distance, as shown in Fig.…”

Nonequilibrium Plasma Aerodynamics

“…The shock wave generated by actuators can be clearly seen, as well as large scale vortex structure as it developed 40 microseconds after the discharge [Correale et al, 2011]. It was observed that after 2-3 discharges the flow pattern changed completely.…”

“…Numerical modeling of SDBD development also shows fast formation of plasma layer and shock wave generation [Unfer&Boeuf, 2009;Starikovskii et al, 2009]. The process of nanosecond pulsed plasma layer interaction with the flow, formation of perturbations and vortices, and flow re-attachment was investigated in details in [Correale et al, 2011]. A model of NACA 63-618 airfoil with the chord of 20 cm and span of 40 cm with the actuator applied was used for experiments.…”

“…Thus, nanosecond pulsed discharges have demonstrated an extremely high efficiency of operation for aerodynamic plasma actuators over a very wide velocity (M = 0.03 -0.75) and Reynolds number (Re = 10 4 -210 6 ) range. For further technological development, it is extremely important to understand the physics of the nanosecond plasma actuator and differences between different types of SDBD in terms of their efficiencies [Roupassov et al, 2008a[Roupassov et al, ,2008bNikipelov et al, 2009;Correale et al, 2011;Rios et al, 2011]. .…”