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Development of plasma actuators for high-speed flow control based on nanosecond repetitively pulsed dielectric barrier dischargesAarthi Devarajan (5930600) 10 June 2019 (has links)
Over the past few decades, surface dielectric barrier discharge (SDBD)
actuators have been studied extensively as aerodynamic flow control devices. There
has been extensive research on producing SDBD plasmas through excitation by
sinusoidal high voltage in low-speed flows, resulting in local acceleration of
the flow through the electrohydrodynamic (EHD) effect. However, high-speed flow
control using SDBD actuators has not been considered to the same extent.
Control through thermal perturbations appears more promising than using EHD
effects. SDBDs driven by nanosecond repetitively pulsed (NRP) discharges (NRP SDBDs)
can produce rapid localized heating and have been used to produce better flow
reattachment in high-speed flows. While surface actuators based on NRP DBDs
appear promising for high-speed flow control, the physics underlying the
plasma/flow coupling are not well understood and the actuators have yet to be
fully characterized or optimized. In
particular, methods for tailoring the plasma characteristics by varying the
actuator’s electrical or geometrical characteristics have not been thoroughly
explored.<div>In the current work, NRP SDBD
actuators for control of high-speed flows are developed and characterized. As
discussed previously, it is believed that the mechanism for high-speed flow
control by these plasmas is thermal perturbations from rapid localized heating.
Therefore, the goal is to design actuators that produce well-defined
filamentary discharges which provide controlled local heating. The electrical
parameters (pulse duration, PRF, and polarity) and electrode geometries are
varied and the optimal configurations for producing such plasma filaments over
a range of ambient pressures are identified. In particular, single and double
sawtooth shaped electrodes are investigated since the enhanced electric field
at the electrode tips may permit easier production of “strong” (i.e. higher
temperature) filaments with well-defined spacing, even at low pressure.
Time-resolved measurements of the gas temperature in the plasma will be
obtained using optical emission spectroscopy (OES) to assess the thermal
perturbations produced by the actuators. To the author’s knowledge, these will
be the first such measurements of temperature perturbations induced by NRP
SDBDs. The plasma structure and temperature measurements will be correlated
with schlieren visualization of the shock waves and localized flow field
induced by the discharges. Finally, the optimized actuators will be integrated
into a high-speed flat plate boundary layer and preliminary assessment of the
effect of the plasma on the boundary layer will be conducted.<br></div>
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A Preliminary Study Of Fields In Split-Electrode Ion TrapsSonalikar, Hrishikesh Shashikant 10 1900 (has links) (PDF)
Ion traps used in mass spectrometers are of two classes. One class consists of traps having three electrode geometries which have rotational symmetry about central axis. They are called axially symmetric ion traps. Paul trap, Cylindrical Ion Trap(CIT) are examples in this class. Other class of traps contain 2D electric field inside them which has same profile along the central axis due to translational symmetry. Linear Ion Trap(LIT) and Rectilinear Ion Trap(RIT) are examples in this class.
In the ideal hyperbolic geometries of Paul trap and LIT, electric field is a perfectly linear function of distance from the center of the trap. But when these ideal geometries are simplified in to simpler geometries of the CIT and the RIT for ease in machining, linearity of field, which is a specialty of Paul trap and LIT is lost.
In this thesis, an effort is made to optimize the field within the traps by using split electrodes. The ring electrode of the CIT and both pairs of electrodes in the RIT are divided into more number of parts. Suitable voltages are applied on these parts to improve the linearity of the field.
This thesis contains six chapters. Chapter 1 contains a background information about mass spectrometry. Chapter 2 discusses the Boundary Element Method (BEM) used to calculate charge distribution and Nelder-Mead method used for optimization. It also shows the calculation of multipoles.
In Chapter 3, two new geometries namely split-electrode RIT and split-electrode CIT are considered with the objective of improving the linearity of electric field inside them. It is shown here that by applying certain external potential on various parts of split electrodes of these geometries, it is possible to improve the linearity of electric field inside them.
In Chapter 4, capacitor models of new geometries proposed in chapter 3 are discussed. The use of external capacitors as a replacement to external power supply is also discussed in this chapter.
InChapter5, study similar to that ofChapter3is carried out by splitting the geometries in more number of parts. The possibility of improved field profile is investigated by applying full potential to some of these parts and keeping other parts at ground potential.
In Chapter 6, concluding remarks are discussed.
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