Typescript (photocopy). / Digitized by Kansas Correctional Industries / Department: Chemistry.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

The primary goal of this research is to assess the effect of synthetic jets on flow separation and provide a feedback control strategy for flow separation using synthetic jets. The feedback control synthesis is conducted based upon CFD simulation for a rounded backward-facing step. The results of the synthetic jet experiments on an airfoil showed that synthetic jets have the potential for controlling the degree of flow separation beyond delaying the onset of flow separation. In the simulation, while the jet is ejected slightly upstream from the separation point, the feedback pressure signal is acquired at a downstream wall point where the vortex is fully developed. Due to the uniqueness of synthetic jets, i.e. "zero-net-mass flux", the profile of synthetic jet velocity cannot be arbitrarily generated. The possible control variables are the magnitude or frequency of the oscillating jet velocity. Consequently, the fluidic system in simulation consists of the actuator model and the NARMAX (Nonlinear Auto Regressive Moving Average with eXogenous inputs) flow model. This system shows a strong nonlinear pressure response to the input jet frequency. Low-pass filtering of the pressure response, introduced for pressure recovery, facilitates a quasi-linear approximation of the system in the frequency domain using the describing function method. The low-pass filter effectively separates the pressure response into two frequency bands. The lower frequency band below the filter pass frequency includes the quasi-linear response targeted by the feedback control and the higher band above the filter stop frequency contains the attenuated higher harmonics, which are treated as nonlinear disturbances. This quasi-linear approximation is utilized to design a PI controller for the fluidic system including the synthetic jet. To ensure one-to-one correspondence of the jet frequency and the filtered pressure response, the upper bound of the jet frequency is set at the frequency of the maximum pressure. The response of the resulting closed loop feedback control system, comprised of a PI controller, low-pass filter, SJA model and NARMAX model, is shown to track the desired pressure command with an improvement in the transient response over the open-loop system.

Thesis (M.S.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains viii, 45 p. : col. ill. Vita. Includes abstract. Includes bibliographical references (p. 39-42).

Thesis (Ph. D.)--Lehigh University, 2000. / Includes bibliographical references and vita.

Thesis (Ph. D.)--Lehigh University, 2003. / Includes vita. Includes bibliographical references (leaves 164-170).

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Thesis (MTech. degree in Mechanical Engineering)--Tshwane University of Technology, 2010. / This study evaluates the use of biodiesel as an alternative fuel for diesel engines. The fuel properties, performance, emission characteristics and combustion characteristics of a four-stroke, four-cylinder water cooled, high speed direct injection (DI) diesel engine operated on biodiesel, 30% biodiesel and 70% biodiesel blended fuels were measured. Results related to the direct use of biodiesel as a diesel engine fuel indicate that this is possible but not preferable because of its high viscosity and cetane number. Biodiesel could be used in the blends with diesel fuel, because most of the measured properties of the biodiesel-diesel blended fuels were close to those of the diesel fuel. It was found that the performance parameters of the biodiesel-diesel blended fuels did not differ greatly from those of diesel fuel. A slight power decrease, with an increase in brake specific fuel consumption (BSFC), was noticed with the blend fuels. Smoke emissions were reduced for the blends while NOx was increased remarkably for the biodiesel-blended fuels. The test results demonstrated that the combustion carbon deposits (CCD) of biodiesel are a little less than that of the diesel fuel. The peak combustion pressure of the B70 blended fuel was found to be the highest amongst the four tested fuels. It is consequently argued that biodiesel appears to offer a potential alternative "greener" energy substitute for fossil fuel.

No description available.

No description available.