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The performance of a high-power small-scale combustion-based fluidic actuator for high-speed flow control applications is characterized with specific focus on comparisons between premixed and nonpremixed operating modes for the device. Momentary (pulsed) actuation jets are produced by the ignition of a mixture of gaseous fuel and oxidizer within a small (cubic centimeter scale) combustion chamber. The combustion process yields a high pressure burst (1 to 3 ms in duration in the typical configurations) and the ejection of a high-speed exhaust jet. The actuation frequency can be continuously varied by independently controlling the flow rate of the fuel/oxidizer and the spark ignition frequency up to a maximum determined by the operating characteristics of the actuator. The actuator performance is characterized by both its peak thrust and net total impulse, with increases in peak jet momentum often two to three orders of magnitude above the baseline steady jet. Results for operation of the device in both premixed and nonpremixed modes are presented and analyzed, with nonpremixed operation typically yielding higher pressures and greater frequency ranges in the present configurations.

Enhanced heat transfer in electronic hardware by direct, small-scale actuation is investigated experimentally in two test bed configurations. The first configuration exploits the unsteady motions induced by a vibrating reed embedded within a heated duct (in contact with hardware that needs cooling) to enhance forced convection transport heat from the duct surfaces. The flow within the duct is either exclusively driven by the reed or, for higher heat flux, is augmented by an induced core flow. The time harmonic motion of the reed results in the regular shedding of vortical structures that interact with the inner surfaces in the absence and presence of a core flow. The second configuration focuses on the effects of small scale motions induced by a synthetic jet on heat transfer within an advanced heat sink. The synthetic jets emanate directly through the base of the heat sink and induce a recirculating flow between the fins, resulting in a lower thermal resistance than what is typically achieved with traditional fans. The unsteady flow characteristics in both configurations are investigated using particle image velocimetry (PIV). Of particular interest are the effects of small-scale motions and enhanced mixing on heat transfer compared to conventional time-invariant flows at similar or higher Reynolds numbers.

Earlier investigations of Combustion Powered Actuation (COMPACT) have demonstrated its utility for high-speed aerodynamic flow control. In this actuation approach, momentary (pulsed) actuation jets are produced by the ignition of a mixture of gaseous fuel and oxidizer within a cubic-centimeter scale chamber. The combustion process yields a high pressure burst and the ejection of a high-speed exhaust jet. The present thesis focuses on characterization of the effects of the internal flow (which is altered through the fuel and oxidizer inlet streams) on mixing and flame propagation within the actuator's combustion chamber, and thereby on actuator operation and performance. A test chamber with a grid of interchangeable air and fuel inlets was used for parametric investigations of the effects of inlet size and location. Actuator performance is characterized using dynamic pressure measurements and phase-locked Particle Image Velocimetry (PIV) of the combustor's internal flow field in the presence and absence of the active combustion process. Over the range tested, increased momentum of the air inlet jet for a given flow rate improves the actuator performance by increasing bulk velocities and small-scale motions within the chamber, thus yielding net higher flame propagation speed and subsequently faster pressure rise and higher pressure peak. Variation in inlet location that results in swirling flow within the chamber yields higher internal pressures while air flow over the spark ignition site yields lower internal pressures and erratic combustion. Improved refill and combustion processes will lead to enhanced performance combustor designs.

Thesis (M.S.)--Florida State University, 2004. / Advisor: Dr. Yousef Haik, Florida State University, College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (viewed June 16, 2004). Includes bibliographical references.

Thesis: Mech. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1979 / Includes bibliographical references. / by Ifiyenia Kececioglu. / Mech. E. / Mech. E. Massachusetts Institute of Technology, Department of Mechanical Engineering

Thesis (M.S.); Submitted to Iowa State Univ., Ames, IA (US); 19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2488" Tugba Kalem. US Department of Energy 12/19/2004. Report is also available in paper and microfiche from NTIS.

This thesis describes a number of studies of microstructured optical resonators, designed with the aim of enhancing the performance of organic semiconductor lasers and exploring potential applications. The methodology involves the micro-engineering of the photonic environment in order to modify the pathways of the emitted light and control the feedback mechanism. The research focuses on designing new organic microstructures using established semi-analytical and numerical methods, developing fabrication techniques using electron-beam lithography, and optically characterising the resulting structures. Control of the feedback mechanism in conjugated polymer lasers is first investigated by studying Distributed Feedback or photonic crystal resonators based on a square feedback lattice. This study identified the diffraction to free space radiation as a major source of loss in current microstructured resonator designs. By cancelling the coupling to free space through the use of different feedback symmetries and diffraction orders, a threshold reduction by almost an order of magnitude is demonstrated. The introduction of mid-gap defect photonic states in an otherwise uniformly periodic structure was studied in Distributed Bragg Reflector (DBR) resonators. This enabled GaN diode pumped polymer lasers to be demonstrated, indicating that the transition from complex excitation sources to more compact systems is possible. Devices for potential applications in the field of optical communications are also explored by demonstrating a polymer DBR laser based on silicon. In this way, the potential for integrating conjugated polymers with silicon photonics is confirmed. Photonic crystal fibres, which have a periodic microstructure in the transverse direction, are explored as an alternative means for controlling the optical properties of organic lasers. Fluidic fibre organic lasers were demonstrated as efficient sources with good spectral purity. In these devices, mechanisms to tune the emission wavelength were explored and the origin of the frequency selection mechanism was investigated.

Algorithms and simulators comprised of SPICE3 as a circuit level simulator and two device simulators EOFLOW and PROPHET for accurate simulation of new types of devices are presented in this thesis. An integration of EOFLOW with SPICE3 creates a capability for efficient simulation of a system containing interconnected electroosmotic flow channels together with control electronics. Using this simulator, an accurate simulation of a complex interconnection of channels has been performed. In addition, various flow control schemes have been evaluated for their effectiveness. Coupling of PROPHET and SPTCE3 allows for the simulation of accurate semiconductor device models. This capability is necessary for critical RF and analog applications. The coupled SPICE3-HB-PROPHET simulator incorporates the harmonic balance algorithm for large-signal frequency domain analysis. Applications of this analysis are demonstrated in the noise coupling between devices sharing the same silicon substrate. / Graduation date: 2003

Two types of rotary gate microvalves are developed for flow modulation in a microfluidic system that operates at high flow rate and/or uses particulate flow. This research work encompasses design, microfabrication, and experimental evaluation of these microvalves in three distinct areas compliant micromechanism, microfluidics, and electromagnetic actuation. The microvalve consists of a suspended gate that rotates in the plane of the chip to regulate flow through the orifices. The gate is suspended by a novel fully-compliant in-plane rotary bistable micromechanism (IPRBM) that advantageously constraints the gate in all other degrees of freedom. Multiple inlet/outlet orifices provide flexibility of operating the microvalve in three different flow/port configurations. The suspended gate is made of a soft magnetic material and is electromagnetically actuated like a rotor in a variable-reluctance stepper motor. Therefore, an external electromagnetic (EM) actuation at the integrated set of posts (stator) causes the gate mass to switch from its default angular position to a second angular position. The microvalve chip is fabricated by electroplating a soft magnetic material, Permalloy (Ni80Fe20) in a sacrificial photoresist mold on a Silicon substrate. The inlet/outlet orifices are then etched into the Silicon substrate from the back-side using deep-reactive ion etch process. Finally, the gate structure is released by stripping the PR and seed layers. This research work presents the realization of a new microvalve design that is distinct from traditional diaphragm-type microvalves. The test results are encouraging and show the potential of these microvalves in effectively modulating flow in microfluidic systems that may not require a tight seal. The microvalve uses a novel in-plane rotary bistable micromechanism that may have other applications such as optical shutters, micro-locks, and passive check valves.