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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.

Data collected with a three-component laser Doppler anemometer system is used to investigate velocity bias. The data is collected in the viscous layer of a fully developed turbulent open water flow at a Reynolds number of 14,766 based on the flow depth. The data collected at a relatively low data rate is analyzed using different correction methods including: straight forward arithmetical averaging, inverse velocity and transit time weighting. The streamwise mean velocity components, the RMS values and the kinematic Reynolds stress are computed using the various weighting methods and are compared to a three-component inverse velocity bias correction model which is taken to represent the "true" values. The three-component inverse velocity bias correction results are in general accordance with the expected behavior in open channel flow and are comparable to the results reported by other researchers employing different experimental techniques. The results of this study show that the bias is sensitive to the correction method used and the theory that the mean streamwise velocity error (without correction) is proportional to the square of the turbulence intensity is confirmed experimentally. Averaging the data without correcting it produced the largest bias while the results from the different inverse velocity techniques were approximately the same although the level of the bias varied with the turbulence variable that was analyzed. As reported in the literature, the transit time weighting method requires accurate determination of the residence time. The relatively poor performance of the transit time method in the present comparison is attributed to the poor accuracy in the measurement of the residence time. Master of Science

The analysis and redesign of a centrifugal impeller for a rocket pump is presented in this thesis. A baseline impeller was designed by Rocketdyne for the NASA Marshall Pump Consortium. Initially, the objective was to reduce the circumferential exit flow distortion of the baseline impeller. Later in the study, the objective became raising the head coefficient of the impeller. The study presented in this thesis was also undertaken to demonstrate current CFD capabilities for impeller design. A literature review includes an overview of centrifugal impeller geometries and configurations. Centrifugal impeller performance and secondary flows are discussed, and a summary of studies on the effects of impeller exit and diffuser inlet velocity distortion on diffuser performance is also presented. The flow calculation details and the results of the baseline impeller flow calculations are described. Fourteen redesigned impeller geometries were analyzed using the Moore Elliptic Flow Program, and the results were compared to the baseline geometry in terms of head rise, losses, and exit flow distortions. A final geometry was chosen; this geometry will be built and tested by Rocketdyne. The results show that backward blade lean can be effective in red using the exit flow distortion of the impeller. Tip slots or holes were not beneficial because of the large inlet boundary layer. Also, it appears possible to raise the head coefficient of the baseline impeller without creating excessive flow distortion. The planned testing is necessary to verify the predictions of the flow code. Master of Science

An experimental evaluation of the breakdown characteristics of the nonuniform electric fields established between two spheres and between two points in a crossflow was conducted and the results were then compared to the breakdown characteristics in quiescent air. The aluminum spheres used in this investigation ranged in diameter from 0.635 em to 2.54 em. The points had a radius of curvature of 0.5 mm. The velocities of the crossflow ranged from 23 mls to 58 mls and the gap distances ranged from 0.5 cm to 2.0 cm. Photography was used to determine the effect of the crossflow on the luminous spark for all electrodes. The sparking voltages in the crossflow were a function of the crossflow velocity, electrode size and gap distance. It was concluded that the most significant increase of sparking voltages in a crossflow, as compared to the same configuration in quiescent air, was for the point-point gap at a distance of 2.0 cm for a 58 mls crossflow. As the electrodes were increased in size, the effect of a given crossflow decreased. For the 2.54 cm spheres with a 58 mls crossflow, there was actually a decrease in the sparking voltage as compared to its counterpart in quiescent air. The photographs showed a significant deflection of the spark in the direction of the crossflow for the point-point gap, but no significant deflection was detected for the other electrode geometries. Master of Science

The effects of a DC voltage on the catalytic combustion rate of natural gas in air over a platinum wire in various configurations is examined. In most cases a high applied voltage reduces and quenches the catalytic reaction. These effects are dependent on the catalyst surface charge density but not on the direction of the field. Greater effects were also observed when the field was applied on the upstream rather than the downstream side of the catalyst. Although the mechanism of this quenching effect is unknown, it is suggested that it involves the generation and diffusion of charged gas-phase species and their interaction with the catalyst surface. Possible quantum effects are also discussed. Further work to verify or refute the mechanisms presented here is suggested. Master of Science

The Earth Radiation Budget Experiment (ERBE) consists of a suite of three scanning and four nonscanning radiometric instruments on each of three satellites which monitor the solar-reflected and Earth-emitted components of the Earth's radiative energy budget. A numerical model has been formulated to study the dynamic behavior and equivalence of the ERBE scanning thermistor bolometer radiometers. The finite-difference method is applied to the detector of the ERBE scanning radiometer to characterize its thermal and electrical dynamic behavior. The thermal analysis confirms the thermal time constant of the instrument claimed by the vendor. The electrical model reveals that the instrument can be very sensitive to spatial variations of the incident thermal radiation. However, the analysis confirms that the hypothesis of equivalence is justified for viewing typical Earth scenes. Master of Science

A laser Doppler Anemometer (LDA) is used to make Reynolds stress measurements in a fully developed, turbulent pipe flow. Traverses are made to measure shear stress, normal stresses, and the correlation coefficient. To assess the accuracy of this system, these measurements are compared with results from other published investigations. The differences between the published reports are discussed to emphasize how much turbulence measurements can vary, even in a well-studied flow. Descriptions are included about LDA theory and turbulence measurement techniques. The techniques discussed include the selection of proper sampling rate, the reduction of statistical bias, the choice of amplification, and optimization practices. Master of Science

A laser Doppler anemometer was used to measure the axial and radial velocity components of hydrogen-air counterflow diffusion flames (CFDF). An axisymmetric opposed jet burner (OJB) used seeded air in one cylindrical tube, and a hydrogen-nitrogen mixture in the opposing cylindrical tube. Velocity measurements were made at four different operating flow rates, and were used to compute the associated strain rate fields. The results were used to qualitatively assess current CFDF modeling schemes, and to expand the knowledge of the fluid velocity field behavior within these flames. The data show behavior qualitatively consistent with most models and experimental studies: the radial velocity is essentially linear with radial position, and the velocity data collapse to functions of axial position only for regions away from the stagnation plane. However, the data also show a variable strain rate field and a relatively thick reaction zone, which are both inconsistent with CFDF models. The axial velocity fields also behaved unexpectedly as the operating flow rates were increased, transitioning from the characteristic N -shaped profile to an asymptotically-approaching profile. Master of Science

The turbulent character of the supersonic wake of a linear cascade of fan airfoils has been studied experimentally using a two-component Laser Doppler Anemometer. The cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the experimental Mach and Reynolds numbers were 2.36 and 4.8 x 10⁶, respectively. In addition to mean flow measurements, Reynolds normal and shear stresses were measured as functions of cascade incidence angle and streamwise location in the near-wake and the far-wake. The extremities of profiles of both the mean and turbulent wake properties were found to be strongly influenced. by upstream shock-boundary-layer-interactions, the strength of which varied with cascade incidence. In contrast, the peak levels of turbulence properties within the shear layer were found to be largely independent of cascade incidence, and could be characterized in terms of the streamwise position only. This fact permitted the determination of the decay of the Reynolds shear stress, the production rate of turbulent kinetic energy, and the turbulent kinetic energy itself with streamwise location. Ph. D.

An investigation has been performed of the flow in a supersonic through-flow fan blade cascade. The blade shapes are those of the baseline supersonic through-flow fan (STFF) under investigation at the NASA Lewis Research Center. Measurements were made at an inlet Mach number of 2.36 over a 15° range of incidence. Flowfield wave patterns were recorded using spark shadowgraph photography and steady-state instrumentation was used to measure blade surface pressure distributions and downstream total and static pressure distributions. A two-dimensional LDV system was used to map the downstream flowfield. From these measurements, the integrated loss coefficients are presented as a function of incidence angle along with analysis indicating the source of losses in the STFF cascade. The results are compared with calculations made using a two-dimensional, cell-centered, finite-volume, Navier-Stokes code with upwind options. Good general agreement is found at design conditions, with lesser agreement at off-design conditions. Analysis of the leading edge shock shows that the leading edge radius is a major source of losses in STFF blades. Losses from the leading edge bluntness are convected downstream into the blade wake, and are difficult to distinguish from viscous losses. Shock losses are estimated to account for 70% to 80% of the losses in the STFF cascade. Ph. D.

Past research at Virginia Tech (VPI) explored the aerodynamic loss of the transonic VPI turbine blade, which 1s based on the pitchline profile of a high pressure turbine blade for a large commercial aircraft gas turbine. The current experiment explores the loss of the VPI blade for different axial solidity ratios near the design point. Ten percent changes in the solidity ratio were accomplished by varying the blade pitch and changing the blade stagger to maintain a constant throat to spacing ratio. Reaction, exit angle and exit Mach number were kept constant with this method. Cascades with three different solidities were tested in VPI’s transonic blowdown wind tunnel. Downstream total pressure loss and static pressure measurements were obtained. In addition, inviscid calculations were made for each case. Static pressure contours and Mach number profiles from the calculations were compared with the experimental results. A ten percent decrease in solidity caused no cascade loss penalty as compared to the Baseline solidity for a wide range of Mach numbers. Calculated blade Mach number profiles agreed well with experimental profiles except on the suction side near the throat and downstream of the shock/boundary layer interaction. Predicted downstream static pressure values agreed well with experimental values, except that the inviscid code tended to over-predict the pressure rise across the suction side shocks. Master of Science

An experimental investigation of reversed flow performance characteristics in a compressor cascade was conducted. The purpose was to gain a fundamental understanding of reversed flow in a compressor blade cascade, and to determine the effects of stagger angle and angle of attack on the reversed flow behavior in the cascade. Tests were conducted at two blade configurations, one to simulate reversed flow in a compressor rotor and one to simulate reversed flow in a compressor inlet guide vane. Three stagger angles were tested for each configuration with an absolute angle of attack range from 70 to 130 degrees. The investigation included total and static pressure measurements upstream and downstream of the cascade as well as blade surface measurements. Aerodynamic performance parameters were presented for a reversed flow cascade. Comparison of corrected total pressure loss curves suggested that blade rows of a compressor subjected to reversed flow may be treated as nearly equal loss producers. A comparison was made between total pressure loss coefficients from this investigation and experimental compressor performance. The total pressure loss coefficients compared favorably in magnitude and curve shape. Master of Science

Tangential supersonic slot injection (M = 1.7) of air into a supersonic air stream (M = 2.91) was studied with a dual hot wire probe. This probe was used to simultaneously determine total temperature and mass flux. Mean profiles across the entire flow field at three axial stations (x/h = 4, 10, 20) were obtained, as well as the temperature and mass flux turbulence intensities. The probe can be used anywhere except at locations where features of the flow are smaller than the separation between the wires (0.18 mm). The calibration of the probe can be repeated with less than a three percent change in calculated Nusselt number. The hot wire probe can also be tuned to obtain a high frequency response. The interaction of a shock wave, caused by a wedge placed on the upper tunnel wall, with the mixing region was investigated. Little change in the mean profiles was observed, but there was a significant increase in turbulence levels. Master of Science

A dual-frequency microwave bum rate measurement system for solid rocket motors has been developed and is described. The system operates in the X-band (8.2-12.4 Ghz) and uses two independent frequencies operating simultaneously to measure the instantaneous bum rate in a solid rocket motor. Modeling of the two frequency system was performed to determine its effectiveness in limiting errors caused by secondary reflections and errors in the estimates of certain material properties, particularly the microwave wavelength in the propellant. Computer simulations based upon the modeling were performed and are presented. Limited laboratory testing of the system was also conducted to determine its ability perform as modeled. Simulations showed that the frequency ratio and the initial motor geometry (propellant thickness and combustion chamber diameter) determined the effectiveness of the system in reducing secondary reflections. Results presented show that higher frequency ratios provided better error reduction. Overall, the simulations showed that a dual frequency system can provide up to a 75% reduction in burn rate error over that returned by a single frequency system. The hardware and software for dual frequency measurements was developed and tested, however, further instrumentation work is required to increase the rate at which data is acquired using the methods presented here. The system presents some advantages over the single frequency method but further work needs to be done to realize its full potential. Master of Science

A three-color, three-component Laser Doppler Anemometer (LOA) capable of making simultaneous measurements of three components of velocity is described, and the use of this LOA to measure three non-orthogonal velocity components in the rotor blade passage of a single-stage axial-flow compressor is reported. Measurements were made at four radial locations from 50% span out to the blade tip, and at seven different axial locations from -0.55 axial chord 1.40 axial chord. Measurements were made at only one throttle setting. The measured velocities are used to determine the flow in the orthogonal axial - tangential - radial, x - t - r, coordinate system of the compressor. Although the mean velocities and entire Reynolds stress tensor are obtained with this system, only the mean velocities are reported. Results are presented in the form of a series of vector plots showing: 1.) the primary flow as projected on the x - t plane and 2.) the secondary flow in the t - r plane. The LOA measurements are shown to agree with pitot probe measurements in the stationary frame and basic secondary flow theory. A detailed error analysis is presented, taking into account both measurement uncertainties and statistical biasing. An analysis is also made of particle lag in the rotating flow of the compressor blade passage. A discussion of the difficulties encountered in making three dimensional velocity measurements in turbomachinery blade passages is presented. Suggestions are made for improving the present system for this task. Master of Science

A high-frequency combination probe was used to measure dynamic flow quality in the test section of the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The probe measures fluctuating stagnation (total) temperature and pressure, static pressure, and flow angles in two orthogonal planes. Simultaneous unsteady temperature and pressure measurements were also made in the settling chamber of the tunnel. The data show that the stagnation temperature fluctuations remain constant, and the stagnation pressure fluctuations increase by a factor of two, as the flow accelerates from the settling chamber to the test section. In the test section, the maximum rms value of the normalized fluctuating velocity is 0.7 percent. Correlation coefficients l failed to show vortlcity, entropy, or sound as the dominant mode of turbulence in the tunnel. At certain tunnel operating conditions, periodic disturbances are seen in the data taken in the test section. A possible cause for the disturbances is found to be acoustic coupling of the test section and plenum chamber via the perforated side walls in the tunnel. The experimental data agree well with the acoustic coupling theory. Master of Science