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A numerical finite-difference model, derived using a control-volume approach, is used to compute the flow and heat transfer characteristics of a confined laminar air jet impinging on an isothermal surface. Four cases are considered, with Re = 250, 500, 650 and 750, and nozzle-to-plate spacing, H/W = 5. At Re = 250, the boundary layer developing on the target plate separates. At Re = 500, the boundary layer develops without separation off the target wall, the jet momentum is sufficient to overcome the adverse outer field and wall effects. The flow is symmetric at these Reynolds numbers, and maximum values for pressure, friction and heat transfer coefficients occur at the stagnation point. The flow at Re = 650 displays asymmetry as the jet buckles, both flow and heat transfer indicate a transition to an unsteady regime. The critical Reynolds number for the onset of unsteady flow is between 585 and 610. When Re is further increased to 750, the jet "buckles" severely and vortices are shed in the high shear regions. The spectral distribution of the velocity in the jet streamwise and spanwise directions at three distinct locations in the jet, point out three dominant frequencies. The lowest frequency, at 3.66 Hz, is associated with the jet "sweeping" the wall, identified as the "flapping" motion. The highest frequency, 12.96 Hz, is related to the "buckling" motion of the jet at the frequency at which vortices are formed in the jet shear layer. As a result of the two combined unsteady modes, the peak heat transfer is enhanced and the lateral extent of the effective cooling is broadened. A distinct demarcation in time averaged Nusselt number was observed between the steady behavior for Re < 600, and the unsteady behavior for Re > 600. The jet subjected to twenty-four types of forcing reveals two cases relevant in terms of flow and heat transfer control. The out-of-phase forcing at the dominant frequency of 10.68 Hz, Re = 650, stabilizes one side of the confined impinging jet. This results in an enhanced wall heat transfer and peculiar behavior of the hydrodynamic field. When forcing out-of-phase at a dominant frequency of 12.96 Hz, Re = 75 0, the jet is stabilized completely. The forcing suppresses the high-amplitude low-frequency "flapping" jet motion, and the jet tip displacement on the target wall captures only the high-frequency low-amplitude oscillatory motion of the jet. The suppression of the jet "flapping" motion leads to a smaller "patch" heat transfer coefficient. However, since the jet washes the target wall without separation, the wall-averaged heat transfer is much higher than the unforced cases. For the out-of-phase forcing at 12.96 Hz, the "patch" heat transfer is 24% lower than the unforced case, while the wall-averaged heat transfer is 35% higher.

This thesis addresses the investigation of mechanisms involved in the transition from laminar to turbulent flow. The flow studied is a compressible flat plate boundary layer at a free stream velocity of M = 4.5. The two-dimensional compressible unsteady Navier Stokes equations are solved numerically in a rectangular region at a distance downstream from the leading edge. Disturbances are introduced by periodical suction and blowing through a slot in the wall. These disturbances propagate downstream in the flow field. At every point in the flow field the response of the flow is analyzed using a Fourier analysis in time. Results obtained are interpreted with reference to linear stability theory. One important result is the existence of multiple undamped waves for one wave frequency. The second important result demonstrates that an amplified wave of a certain frequency can generate disturbances at multiples of its frequency which may then be amplified more strongly.

A facility was designed to perform detailed fluid mechanics and heat transfer experiments in a turbulent channel flow over a two-dimensional obstacle. This document describes the design and fabrication of the air delivery system and uniform heat flux surface. The wind tunnel consists of a plenum section with 6,36 Mesh screens and 4cm long honeycomb, a 6.0 ratio contraction 1.1 8m in length, and a 2.64m long test section with plexiglas test surfaces. The uniform heat transfer surface was designed to be interchangeable with either floor of the test section and consists of eleven panels each instrumented with a heater and thermocouples; 21 to measure surface temperature and 3 to gauge heat losses. The heaters are controlled independently allowing a variety of heating configurations. Both hydrodynamic and heat transfer test surfaces can accommodate a fence of varied thickness and height. The instrumentation necessary to perform measurement and equipment control was assembled and proved to operate properly. Investigations of facility characteristics were performed. These results illustrate areas in which improvements can be achieved with further work, however, in general the system operates as intended.

In 1957, the space race began with the launch of Sputnik. The Soviet Union and the United States fought to be the first to place an object in earth orbit, to maintain it in orbit the longest, and eventually to land humans on the moon. During this time of competition, nothing was done to remove the spent objects or man-made debris from orbit. In recent years, man has become interested in the environment and the effects of his actions on it. This environmental consciousness has begun to extend to NASA and the space program. NASA has realized that the amount of orbited space debris around the earth poses a threat to future manned and unmanned missions. It is for this reason that Dr. Kumar Ramohalli, at the University of Arizona, proposed the concept of an Autonomous Space Professor for Orbital Debris (ASPOD). This thesis is designed to be a summary of the ASPOD spacecraft, what has been done on it, and what still needs to be done.

<p> This project was started in the interest of supplementing existing data on additives to composite solid propellants. The study on the addition of iron and aluminum nanoparticles to composite AP/HTPB propellants was conducted at the Combustion and Energy Systems Laboratory at RPI in the new strand-burner experiment setup. For this study, a large literature review was conducted on history of solid propellant combustion modeling and the empirical results of tests on binders, plasticizers, AP particle size, and additives. </p><p> The study focused on the addition of nano-scale aluminum and iron in small concentrations to AP/HTPB solid propellants with an average AP particle size of 200 microns. Replacing 1% of the propellant's AP with 40-60 nm aluminum particles produced no change in combustive behavior. The addition of 1% 60-80 nm iron particles produced a significant increase in burn rate, although the increase was lesser at higher pressures. These results are summarized in Table 2. The increase in the burn rate at all pressures due to the addition of iron nanoparticles warranted further study on the effect of concentration of iron. Tests conducted at 10 atm showed that the mean regression rate varied with iron concentration, peaking at 1% and 3%. Regardless of the iron concentration, the regression rate was higher than the baseline AP/HTPB propellants. These results are summarized in Table 3.</p>

There is now a substantial body of theoretical and experimental evidence that the dominant part of the turbulent mixing noise of supersonic jets is generated directly by the large turbulence structures/instability waves of the jet flow. The relationship between the instability waves and noise of hot jets at moderate supersonic Mach number is examined in Chapters 1 and 2. It is found that the highest sound-pressure-level of the far-field noise occurs at a direction and frequency that closely match the Mach wave radiation direction and frequency of the most amplified instability wave of the jet. The calculations show that for jet Mach number up to 2.0 and jet total temperature to ambient temperature ratio up to 2.5, the Kelvin-Helmholtz instability waves always grow to a higher amplitude than the supersonic instability wave. Numerical results indicate that for hot jets the most amplified wave invariably belongs to the helical mode Kelvin-Helmholtz instability wave. For lower speed hot jets with jet static temperature higher than or equal to the ambient temperature there is also a fair correlation between the Strouhal number at the peak sound-pressure level of the far-field noise and that of the most amplified instability wave. / In Chapters 3, 4, 5 and 6, a broadband jet noise theory is constructed. In this theory, the compressible flow equations with eddy viscosity are used to calculate the wave propagation characteristics of the instability waves. These equations are solved by the method of matched asymptotic expansions. The inner solution is the instability wave solution. The outer solution gives the associated acoustic field. The amplitudes of the instability waves are assumed to be stochastic random functions. The statistical properties of the random amplitude function are determined by the requirement that the wave spectrum at the nozzle exit has no intrinsic length and time scales. The present theory can predict the dominant part of jet mixing noise from first principles up to a single multiplicative constant. The spectra and directivities of a Mach 2 jet at total temperatures of 500K and 1114K are calculated. The numerical results agree favorably with experimental measurements. / Source: Dissertation Abstracts International, Volume: 54-12, Section: B, page: 6317. / Major Professor: Christopher K. W. Tam. / Thesis (Ph.D.)--The Florida State University, 1993.

The free shear layer coming out from the lip of an asymmetric two-dimensional supersonic nozzle in a Ludweig tube wind tunnel is investigated. Newly developed procedures for Laser Induced Fluorescence (LIF) of NO$\sb2$ are utilized as the main diagnostic technique in conjunction with the new Direct Estimation Velocimetry (DEV) to produce density and velocity measurements at sampling rates in excess of 2 MHz. Both two- and three-dimensional configurations of LIF are utilized with success. Comparable measurements of density and velocity over several runs prove to be readily reproducible in their turbulent parameters. Three-dimensional LDV is used to calibrate DEV and shows excellent agreement. For the first time ever at these sampling rates, the cross-stream component of vorticity is measured and shows periodic "bursts", which is a consistent observation with other researchers. PLIF signals, recorded on an intensified framing camera equipped with a Charge-Coupled Device (CCD) using a thin sheet of laser light, show the nonturbulent nature of the flow at the beginning of the free shear layer and large streaky structures at the center of the shear layer. The characteristic scales of the existing turbulence are calculated using the spectral and dimensional analyses, and shown to be consistent with scales for the expected turbulence. Collected data are tested for the ergodic hypothesis of turbulence and the spectral indices for all different runs and different intervals of time fall in to a range of 1.65 $\pm$.05. Each component of the Reynolds stress tensor is measured and subsequently the total Reynolds stresses terms are computed; contribution of the turbulence compressibilty terms to the total Reynolds stress is measured to be 68%; the triple correlation term, $\rm\langle\rho\sp\prime u\sb{i}\sp\prime u\sb{j}\sp\prime\rangle,$ is measured for the first time / in this type of a flow and accounts only for 0.475 $\pm$ 0.325%. Seven different closure models as suggested by various researchers are evaluated using the results obtained in the present investigation. The mean value of the triple correlation terms measured is 0.029 $\pm$ 0.04 which appears to tentatively confirm the natural closure of turbulence theory which predicts vanishing triple, and higher order correlation terms. / Source: Dissertation Abstracts International, Volume: 57-02, Section: B, page: 1382. / Major Professor: Joseph A. Johnson, III. / Thesis (Ph.D.)--The Florida State University, 1996.