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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.

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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Extensive measurements using hot-wire anemometry were carried out for single jet, tandem jets, and side-by-side jets for a velocity ratio of 2, and a jet spacing of 4 for the latter two cases. The measurements yielded axial mean velocity, turbulence intensities, and Reynolds stresses for four downstream stations for the single jet and two downstream stations for the double jet. A preliminary study of the one-dimensional frequency spectra and flow visualization using a tuft wire were also performed. An analytical study using a momentum-integral approach was also carried out in order to predict the gross jet properties such as the jet trajectories, the jet growth, and the mean jet velocity and the mean jet temperature. The jets showed considerable influence on each other for the jet spacing of four jet diameters. An upward shift of the merged jet trajectory, and a widening of the jet crosssection in both directions for the tandem jets as compared to the single jet, were observed. Good correlation between the mean velocity gradients and Reynolds shear stresses were found to exist. The detailed flow structure was found to be very similar for the single jet and tandem jet cases for the downstream stations. The distribution of the one-dimensional energy spectra showed spatial and/or configurational dependence; however, no discernible variation of the frequency corresponding to the peak energy was observed. The flow visualization study showed the existence of circulatory flow in the cross-planes. The analytical study gave results which agreed very well with experimental data. / Ph. D.

The problem of laminar jet reattachment to an inclined flat plate was attacked by the application of the momentum equation at the reattachment point. The pressure distribution within the separation bubble was considered in the analysis as well as the initial state of development of the reattaching jet. The assumption was also made that reattachment angle was independent of Reynolds number for a given plate inclination. A general solution was developed in which reattachment distance was determined to be directly proportional to Reynolds number. The theory correlated moderately well with experiment at a plate inclination of 30°, but it clearly failed at all other angles of inclination. It was shown that the initial state of jet · development had a first order effect on the reattachment phenomenon. / M. S.