Philip Peschke

Experimental Investigation of Pulsed Dielectric Barrier Discharge Actuators in Sub- and Transonic Flow

Experiments were conducted in order to investigate the ability of nanosecond pulsed dielectric barrier discharge (ns-DBD) actuators to control flow on airfoils in subsonic and transonic flow (up to Ma1 = 0.75, Re = 1.35 • 10^6). A NACA 0015 profile equipped with a leading edge mounted ns-DBD actuator was investigated up to Re = 2.3 • 10^5 (u1 = 24 m/s). Measurements of the surface pressure distribution clearly confirm the actuator’s potential to delay leading edge separation. In the following the impact on the control authority of different voltage pulse parameters, such as voltage amplitude, actuation frequency and rise/fall time of the pulse were investigated. The experiments in transonic flow were conducted on a NACA 3506 compressor blade profile. A ns-DBD actuator was placed at x/c = 0.33 where the foot of the shock-wave and boundary-layer separation was observed. Schlieren flow visualization showed the shock-wave boundary-layer interaction and was used to investigate the actuator’s effect on the shock position and shape. A high-speed camera allowed to acquire schlieren images at high acquisition rates and investigate as well the movement of the shock in the frequency domain. These results were verified with measurements of the static pressure at the side wall using unsteady pressure transducers.

Effects of High Voltage Pulsed DBD on the Aerodynamic Performances in Subsonic and Transonic Conditions

The paper presents the results of a research activity that aims to investigate the control effect of fast rising pulse Dielectric Barrier Discharge actuators (DBD) in high speed flow conditions. At this aim, several experimental tests have been performed on a 2D wind tunnel model in subsonic and transonic conditions to collect information concerning effects of DBD actuators on the main aerodynamic aerofoil performance. The Mach number was varied between 0.4 and 0.85 at angles of attack ranging between -2° and 8° and Reynolds numbers between Re=1.7∙10 6 and Re=2.5∙10 6 . The aerofoil geometry selected for these tests was the supercritical BAC3-11 profile with 11% of maximum thickness. During the experiments, quantitative measurements have been made through steady and instantaneous pressure sensors. In particular, 45 pressure taps and 10 high frequency pressure transducers were installed on the surface of the model. The experimental data were used to develop and validate numerical tools, able to predict the plasma behaviour in presence of convective fields and, therefore, to support the design and setting of more effectiveness DBD actuator. A Computational Fluid Dynamics (CFD) solver developed at CIRA has been used for numerical simulations. A theoretical model for dielectric barrier discharge (DBD) via bodyforce and power density terms has been implemented in order to support the experimental test campaign.

Investigation of Nanosecond Pulse Dielectric Barrier Discharges in Still Air and in Transonic Flow by Optical Methods

In the present study the interaction of nanosecond pulsed dielectric barrier discharge (ns-DBD) actuators with aerodynamic flow up to transonic velocities was investigated. The primary focus was on the influence of the flow on the discharge and the effects of the discharge itself. In addition, the influence of the ns-DBD on a shock-wave was studied. The aim was to improve the understanding of the plasma-flow interaction, a topic that is not yet fully understood, in particular for ns-DBD. The actuator was integrated in two different models, a NACA 3506 compressor blade profile and a bump geometry at the bottom of the wind tunnel. The effect of the rapid energy deposition close to the discharge was examined with the phase-locked schlieren visualisation technique. Images of the plasma acquired with short exposure times revealed information on the discharge evolution. The results show a significant effect of the flow on the discharge characteristics, in particular due to the drop of static pressure. On the other hand, no significant effect of the ns-DBD on the flow was observed due to unfavourable flow conditions, which underlines the importance of the actuator’s placement.

Impact of ns-DBD plasma actuation on the boundary layer transition using convective heat transfer measurements

This paper demonstrates that the impact of nanosecond pulsed dielectric barrier discharge (ns-DBD) actuators on the structure of the boundary layer can be investigated using quantitative convective heat transfer measurements. For the experiments, the flow over a flat plate with a C4 leading edge thickness distribution was examined at low speed incompressible flow (6.6–11.5 m s−1). An ns-DBD plasma actuator was mounted 5 mm downstream of the leading edge and several experiments were conducted giving particular emphasis on the effect of actuation frequency and the freestream velocity. Local heat transfer distributions were measured using the transient liquid crystal technique with and without plasma activated. As a result, any effect of plasma on the structure of the boundary layer is interpreted by local heat transfer coefficient distributions which are compared with laminar and turbulent boundary layer correlations. The heat transfer results, which are also confirmed by hot-wire measurements, show the considerable effect of the actuation frequency on the location of the transition point elucidating that liquid crystal thermography is a promising method for investigating plasma-flow interactions very close to the wall. Additionally, the hot-wire measurements indicate possible velocity oscillations in the near wall flow due to plasma activation.

OES Characterization of Steamers in a Nanosecond Pulsed SBDB Using N2 and Ar Transitions

The characterization of non-thermal homogeneous plasmas is possible using optical emission spectroscopy (OES), notably by estimating the reduced electric field. This method was applied to characterize streamers generated by a nanosecond pulsed surface dielectric barrier discharge (SDBD) operated in quiescent air at atmospheric pressure and also at 0.5 atm. The average reduced electric field associated with the surface streamers was determined using four different sets of transitions occurring in air plasmas, the first negative system (FNS) of N2 + , the first positive system (FPS) and second positive system (SPS) of N2 and argon transitions 2px − 1sy. The analysis of the results allowed to critically assess the validity of the estimated reduced electric field for the present conditions. It is shown experimentally that the inhomogeneous nature of the streamer head influences significantly the estimation of the reduced electric field. Moreover, the estimated reduced electric field is not sufficient to characterize the processes taking place in the streamer head, due to the steep variation of both the reduced electric field E/N and the electron density ne in space and time. To overcome this limitation, a new method is proposed to take into account the spatial structure of a streamer head. The applicability of the new method is demonstrated for these experimental conditions and shows a very good agreement for the transitions tested.