Craig Hale

Imaging gas and plasma interactions in the surface-chemical modification of polymers using micro-plasma jets

This paper reports on the correlation between gas flow and plasma behaviour in the outflow of a micro-atmospheric pressure plasma jet operating in helium using both 2D optical imaging and Schlieren photography. Schlieren photography shows that the helium outflow changes from laminar to turbulent conditions after distances between 20 and 50 mm from the nozzle. Above a flow rate of 1.4 slm, the length of the laminar region decreases with increasing flow rate. However, by contrast the visible plasma plume increases in length with increasing flow rate until its extension just exceeds that of the laminar region. At this point, the plasma becomes turbulent and its length decreases. Exposing polystyrene (PS) samples to the plasma jet significantly alters the water contact angle in a defined area, with the hydrophobic PS surface becoming more hydrophilic. This modification occurs both with and without direct contact of the visible glow on the surface. The radius of the treated area is much larger than the width of the visible jet but much smaller than the area of the turbulence on the surface. The treated area reduces with increasing nozzle–substrate distance.

Schlieren Photography of the Outflow From a Plasma Jet

Using Schlieren photography, the helium outflow configuration from a fine capillary-based microplasma jet discharge has been captured for free-stream conditions. The transition from laminar to turbulent flow is clearly identified with and without operation of the plasma. At a flow rate of 2.3 L·min-1 with no plasma operating, this transition occurs 54 mm from the nozzle; however, with plasma struck (peak voltages of 8 kVp-p), this reduces to 40 mm.

The Influence of Electrode Configuration and Dielectric Temperature on Plasma Actuator Performance

In this paper further experimental studies have been conducted for a new con guration of the Multiple Encapsulated Electrodes (MEE) actuator. The MEE actuator consists of an encapsulated electrode split into smaller electrodes and distributed through the dielectric. This type of actuator has been shown previously to produce performance superior to the standard actuator design. This makes them more desirable as ow control devices. Using particle image velocimetry to visualize and quantify the ow eld, the new con guration has been applied individually and in pairs, and compared to another MEE con guration and the standard design. The results show that further manipulation of the encapsulated electrode can improve performance when compared to other MEE designs. The actuators have also been operated under three di erent surface temperature conditions. Operating the actuator at lower temperatures provided improved performance by increasing the induced velocity while lowering the power consumption.

Multiple Encapsulated Electrode Plasma Actuators to Influence the Induced Velocity: Further Configurations

Further configurations of the Multiple Encapsulated Electrode plasma actuators have been investigated. The actuators consist of 2 encapsulated electrodes distributed throughout the dielectric layer to influence the electric field distribution. The velocity fields have been recorded using PIV in a quiescent environment. Various velocity profiles have been extracted and used to compare the performance of the different configurations. The voltage and current characteristics, from which the power can be calculated, has also been recorded. The plasma is seen to couple momentum into the quiescent environment with the amount of coupling being influenced by the electrode configurations. The highest induced velocity achieved was 91.2% greater than the baseline case while using only 26.2% more power, at the same input voltage.

Plasma Actuators with Multiple Encapsulated Electrodes to Influence the Induced Velocity

A new configuration of plasma actuator, that uses multiple encapsulated electrodes has been compared to a corresponding standard configuration. The velocity fields generated have been recorded using PIV and the voltages and currents recorded. It has been shown that the encapsulated electrode affects the induced jet characteristics. The position to the initial jet has been manipulated as has the initial jet thickness. Velocity is seen to increase linearly along the encapsulated electrode, while momentum coupling has been achieved 15mm downstream of the encapsulated electrode. The magnitude of the induced velocity was also affected with all of the multiple encapsulated electrode actuators producing induced velocities greater than the baseline case. The highest induced velocity was 36.5% greater than the baseline case at the same input voltage while requiring 11.7% less power.

Flow Control of a NACA0015 Airfoil in a Turbulent Wake Using Plasma Actuators

This work involves the control of leading edge ow separation occurring over an aerofoil at high angle of attack. It also contains the documentation of boundary layer transition from the laminar to the turbulent state over an aerofoil facing the wake of circular cylinder. A symmetric NACA 0015 aerofoil was used because of its well documented stall properties. Surface pressure measurement was used to determine the lift coe cient. Mean velocity pro les of the wake of the aerofoil were used for drag coe cient calculation. The experiment was carried on in the chord Reynolds number of 1:5 10. A Multiple Encapsulated Electrode (MEE) plasma actuator was embedded at the leading edge of the aerofoil. It was found that it can delay separation and increase the stall angle. It was accompanied by improvement of the aerodynamic coe cient of aerofoil facing the wake.

Optimization of Induced Velocity for Plasma Actuator with Multiple Encapsulated Electrodes using Response Surface Methodology

In design problem such as a new configuration of plasma actuator for maximizing the velocity of the airflow, experimental setup is done by an ad-hoc procedure. This provides the researcher with a relationship of the input parameters (width of the electrode, distance of the electrodes, the voltage and etc) and the velocity. As the experiments are time consuming and expensive in most of the cases, the above method is not always a reasonable approach in finding the optimal plasma configuration. In this paper response surface methodology, a surrogate modelling approach, is used to allow a systematic investigation in setting the experiments and finding the optimal plasma configuration. This allows the researcher to consider the uncertainty in observation and find a reliable approximate model for the induced velocity. Furthermore, the velocity of the airflow is modelled with small while enough number of experimental setups. The model is validated with the experimental data.