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A spatial linear stability analysis of circular and elliptical jets has been carried out. For the circular jet, the Michalke's shooting method has been extended to the case with a swirling basic flow. For the elliptical jet, an algebraic eigenvalue problem has been formulated by applying the Chebyshev and Fourier spectral collocation method to the disturbance equations of the flow expressed in a generalized cylindrical coordinate system. The resulting algebraic eigenvalue problem was solved using the inverse power method. The approach developed is capable of handling the influences of different distributions of the momentum thickness, swirl, and heat release. In addition to studying the stability properties of the elliptical jet in comparison with those of a circular jet, the linear stability analysis has been used to obtain the insight into the entrainment process. A possible way to enhance the entrainment of elliptical jets has been suggested. / Ph. D.

In this experimental research, jets injected from a flat plate into a crossflow at large angles have been studied. Results were obtained as surface pressure distributions and mean velocity vector plots and turbulence intensities and Reynolds stresses in the jet plume. Rectangular jets (length/width=4) and circular jets were tested. The rectangular jets were aligned streamwise as single and side-by-side dual jets. For the rectangular jets, the jet injection angles were 90° and 60°. The circular jet results were obtained for a single circular jet injected at a 90° angle. Different types of the circular jets were studied with low exit turbulence, high exit turbulence, 40 % swirl and 58 % swirl. The surface pressure distribution results were obtained for jet to freestream velocity ratios of 2.2, 4 and 8 for most of the cases mentioned. Mean velocity vector plots were obtained for the 90° and 60° side-by-side dual rectangular jets and all the circular jet types, mainly for the jet to freestream velocity ratio of 4. Turbulence results were obtained for a jet to freestream velocity ratio of 4 for the 90° and 60° side-by-side dual rectangular jets and for the circular jet with low exit turbulence cases. The results showed that the higher exit turbulence reduced the penetration height, and it also reduced the surface area influenced by the negative pressures. The swirl caused asymmetric pressure distributions, and the swirl effects were more pronounced for lower velocity ratios. The rectangular jets featured strong negative pressure peaks near the front nozzle corners. The 60° rectangular jets produced lower magnitude negative pressures which are distributed over a lesser area when compared to the 90° rectangular jets. / Ph. D. / incomplete_metadata

Contrary to common intuition, free jets of fluid can ``bounce'' off each other on collision in mid-air, through the effect of a lubricating air film that separates the jets. While there has been much work on coalescing jets of fluid and non-coalescence in other systems like drop-drop, drop on a bath, jet on a bath, non-coalescence of fluid jets has been little studied. A simple experimental setup was developed to stably demonstrate and study the non-coalescence of jets upon collision. This thesis presents the results of an experimental investigation of oblique collision between two fluid jets. The transition from bouncing to coalescence of jets is examined for various jet sizes and angles. Results indicate that the transition from bouncing to coalescence can be rationalized in terms of critical value of the dimensionless parameter Normal Weber Number, which represents the ratio between inertial and surface tension forces. A parametric study of the characteristic of bouncing jets, conducted by varying the nozzle diameter, jet velocity, angle of inclination and fluid viscosity reveals the scaling laws for the quantities involved such as contact time. These scaling laws help us in elucidating the role of various physical forces at play such as viscous stresses, capillary force and inertia / Master of Science

M. S.

In this investigation, an approach to studying hot-flow subsonic cross-stream fuel injection problems with a less complex and less costly cold-flow facility was developed and implemented. An actual ramjet combustion chamber fuel injection problem was proposed where ambient temperature fuel was injected into a heated airstream. This case was transformed through similarity parameters involving injection and freestream properties to a simulated case where a chilled injectant was injected into an ambient subsonic airstream. This task was accomplished through injection of chilled Freon-12 into the Virginia Tech 23 x 23 cm. blow-down wind tunnel at a freestream Mach number of 0.44. The freestream stagnation pressure and temperature were held at 2.5 atm. and 300°K respectively. The resulting spray plume was carefully examined and documented with photographs and droplet measurements. The results showed a clear picture of the mechanisms of jet decomposition and vaporization. Immediately after injection a vapor cloud was formed in the jet plume, which dissipated downstream leaving droplets on the order of 8 to 10 microns in diameter for the conditions examined. / Master of Science

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