Sven Grundmann

Power consumption, discharge capacitance and light emission as measures for thrust production of dielectric barrier discharge plasma actuators

A new procedure of determining the time resolved capacitance of a plasma actuator during operation is introduced, representing a simple diagnostic tool that provides insight into the phenomenological behavior of plasma actuators. The procedure is demonstrated by presenting example correlations between consumed electrical energy, size of the plasma region, and the operating voltage. It is shown that the capacitance of a plasma actuator is considerably increased by the presence of the plasma; hence a system that has previously been impedance matched can be considerably de-tuned when varying the operating voltage of the actuator. Such information is fundamental for any attempts to increase the energy efficiency of plasma-actuator systems. A combined analysis of the capacitance, light emission, size of the plasma region, force production, and power consumption is presented.

Velocity-information-based force-term estimation of dielectric-barrier discharge plasma actuators

Particle image velocimetry measurements in close proximity to dielectric-barrier discharge plasma actuators are conducted to quantify the momentum transfer of the plasma to the surrounding air flow. Based on these data a comparative analysis of six existing approaches to estimate the induced body force is presented. Integral methods calculate an integral value for the actuator force based on the momentum-balance equation. Insight into the spatial distribution of the body force is provided by differential methods, which are based either on the Navier–Stokes equations or on the vorticity equation. It is demonstrated that the intensity as well as the domain of the force increase with increasing operating power levels. Emphasis is also placed on the issue of self-induced drag. It is shown that 30% of the induced momentum is consumed by wall friction. All results are validated with previously obtained balance force data and luminosity analysis of identical actuators.

Delay of Boundary-Layer Transition Using Plasma Actuators

In the present work two different methods are presented to attenuate artificially excited perturbations in a laminar boundary layer using plasma actuators resulting in a delay of transition. In both cases Tollmien-Schlichting waves are artificially excited by a vibrating surface driven by an electromagnetic actuator flush mounted in a flat plate. The waves were amplified by an adverse pressure gradient induced by an insert on the upper wall of the test section. One or two control plasma actuators are positioned downstream of the excitation actuator to attenuate the waves by imparting a steady force or an unsteady force into the boundary layer. The steadily operated actuators change the boundary-layer profile locally resulting in a damping of the oscillations in the boundary layer. If the control actuator is operated in pulsed mode it depends on the phase shift between the oscillations and the actuator if the oscillations are amplified or cancelled. Operated in pulsed mode with correct frequency, phase shift and amplitude the energy consumption necessary to achieve the same attenuation as achieved with the steadily operated actuator is only 12 percent of the steady actuator.

PIV-based estimation of DBD plasma-actuator force terms

PIV measurements in close proximity to dielectric-barrier discharge plasma actuators have been conducted to quantify the momentum transfer of the plasma to the surrounding air flow. Based on this data a comparative analysis of six existing approaches to estimate the induced body force is presented. Integral methods calculate an integral value for the actuator force based on the momentum balance equation. Insight into the spatial distribution of the body force is provided by differential methods, which are based either on the Navier-Stokes equations or on the vorticity equation. It is demonstrated that the intensity as well as the domain of the force increase with increasing operating power levels. Emphasis is also placed on the issue of self-induced drag. It is shown that 30% of the induced momentum is consumed by wall friction. All results are validated with previously obtained balance force data and luminosity analysis of the identical actuators.

On the classification of dielectric barrier discharge plasma actuators: A comprehensive performance evaluation study

The increasing popularity and maturity of plasma actuators for many flow control applications requires a common standard for plasma actuator performance evaluation. In the present work, a comprehensive comparative study of existing and new evaluation measures is presented, based on results from identical plasma-actuator configurations. A power-flow diagram is introduced that covers the entire range of power stages from the energy source to the flow-control success. All individual power stages are explained, existing controversial definitions are clarified, and an evaluation guideline is applied to previously obtained data. Finally, the defined systematic analysis is applied to the results of a recently conducted plasma-actuator in-flight experiment.

Experimental and Numerical Investigations of Boundary-Layer Influence Using Plasma-Actuators

This is a fundamental study about the influence of plasma-actuators on boundary-layer flows, including both experimental and numerical investigations. The first set of experiments is conducted in quiescent air and these results are used to calibrate a numerical model which simulates the plasma-actuator in an existing RANS (Reynolds Averaged Navier-Stokes) code. The second set of experiments involves a flat-plate boundary layer at various free-stream velocities, where the actuator adds momentum to the boundary layer. The previously calibrated numerical model is used to simulate the influence of the actuator on the boundary layer. The agreement between simulation and experiment is very good and the simulations with the new model be considered a reliable predictive tool.

Airflow influence on the discharge performance of dielectric barrier discharge plasma actuators

In the present work, the effect of the airflow on the performance of dielectric barrier discharge plasma-actuators is investigated experimentally. In order to analyze the actuator’s performance, luminosity measurements have been carried out simultaneously with the recording of the relevant electrical parameters. A performance drop of about 10% is observed for the entire measured parameter range at a flow speed of M = 0.145 (U∞=50 m/s). This insight is of particular importance, since the plasma-actuator control authority is already significantly reduced at this modest speed level. The results at higher Mach numbers (0.4<M<0.8) reveal an even more pronounced reduction of about 30%. From the combined analysis, the conclusion is drawn that the decreasing electrical performance PA correlates closely with the decreasing luminosity peak intensity G for increasing airflow velocities. Two non-dimensional scaling numbers are proposed to characterize and quantify the airflow influence. It is demonstrated that these...

Dielectric Barrier Discharge Plasma Actuators for In-Flight Transition Delay

A single dielectric barrier discharge plasma actuator is employed for flow control on the pressure side of a natural laminar flow wing section under free-flight conditions. A full-sized motorized glider is equipped with the flow-control device and data-acquisition hardware to quantify the impact of the actuator on boundary-layer transition. A transition delay of approximately 3% chord is achieved, quantified by microphone and hot-wire measurements. Simultaneously, the influence of the variable ambient conditions on the flow-control performance is characterized. A closed-loop control algorithm enables constant actuator performance, despite varying humidity, temperature, and density throughout the test flights. The energy efficiency of the flow-control approach is estimated, providing a positive outlook for further improvements and a net benefit of transition control. Finally, a numerical procedure is presented to quantitatively estimate the effect of dielectric barrier discharge actuation on boundary-layer...

Unmanned Aerial Vehicle (UAV) with Plasma Actuators for Separation Control

Plasma actuators are well known since many years. A large number of publications show the application of plasma actuators for various flow-control applications. The actuators are applied for the tripping of the laminar-to-turbulent transition of boundary layers, for the active cancellation of Tollmien-Schlichting waves, for the delay of the turbulent-to-laminar transition, for the control of jets and most works concentrate on the separation control of airfoils, wings or turbine blades. All experiments have been performed in wind tunnels and labs, since the high voltage generators usually consist of large and heavy equipment. In the present work the first unmanned aerial vehicle (UAV) equipped with a high voltage generator and plasma actuators for the control of the flow separation on the wings is presented. The small plane demonstrates the applicability of the plasma-actuator technology for real planes of reduced size and paves the way for full-size flight experiments.

In-flight Transition Delay with DBD Plasma Actuators

A single dielectric barrier discharge plasma actuator is employed for flow control on the pressure side of a natural laminar flow wing section under free-flight conditions. A full sized motorized glider is equipped with the flow control device and data acquisition hardware to quantify the impact of the actuator on boundary-layer transition. A transition delay of approximately 3% chord is achieved, quantified by microphone and hot-wire measurements. Simultaneously, the influence of the variable ambient conditions on the flow control performance is characterized. A closed-loop control algorithm enables constant actuator performance, despite varying humidity, temperature and density throughout the test flights. The energy efficiency of the flow control approach is estimated, providing a positive outlook for further improvements and a net benefit of transition control.