Turbulent liquid sheets have been proposed to protect solid structures in fusion power plants by attenuating damaging radiation. For the High-Yield Lithium-Injection Fusion Energy (HYLIFE-II) inertial fusion energy (IFE) power plant concept, arrays of molten-salt sheets form a sacrificial barrier between the fusion event and the chamber first wall while permitting target injection and ignition. Thick liquid protection can help make fusion energy commercially attractive by reducing chamber size and prolonging chamber lifetime. Establishing an experimental design database for this basic building block flow will provide valuable information about various thick liquid protection schemes and allow reactor designers to establish acceptable tolerances between chamber components. Turbulent water sheets issuing downwards into ambient air were studied experimentally at Reynolds numbers of 53,000 ??0,000 and Weber numbers of 2,900 ??,000 based on average velocity and the short dimension of the nozzle exit ( and delta). Initial conditions were quantified by the streamwise (x) and transverse (z) velocity components using laser-Doppler velocimetry just upstream of the nozzle exit. Characterization of the mean free-surface position and free-surface fluctuations, or surface ripple, and estimation of the amount of mass ejected as droplets from the free surface were quantified in the near-field (within 25 and delta of the nozzle exit). Surface ripple and mean sheet geometry were determined directly from planar laser-induced fluorescence visualizations of the free surface. The droplets due to the turbulent breakup of the jet, termed here the hydrodynamic source term, were measured using a simple collection technique to within 1 and delta of the nominal free surface of the jet. The influence of various passive flow control techniques such as removing low-momentum fluid at the free surface (boundary-layer cutting) on sheet geometry, surface ripple, and turbulent breakup were also quantified. The data obtained in this research will allow designers of inertial fusion energy systems to identify the parameter ranges necessary for successful implementation of the thick liquid wall protection system.

Foundational approaches for realizing practical, non-intrusive measurements using filtered Rayleigh scattering (FRS) are presented and analyzed for the multi-property quantification of internal flow fields. Validation is challenging in applying computational fluid dynamics (CFD) solutions to real-world scenarios, necessitating benchmark measurements with well-defined uncertainties. The ideal instrument for achieving the required measurements should be non-intrusive and require no particulate or gas seeding. One approach that satisfies these requirements is filtered Rayleigh scattering. FRS is a laser-based optical diagnostic technique that allows for the simultaneous, non-intrusive measurement of three-component velocity, static temperature, and static density everywhere within a two-dimensional plane illuminated by laser light without using any form of flow seeding. The major disadvantage of FRS is that it is very susceptible to signal contamination from particles and surfaces illuminated by the probing laser source. The effects of these contamination sources of the FRS signal are quantified as a function of their intensity relative to the Rayleigh scattered light. As the most significant contributor to Rayleigh scattering contamination, methods for reducing geometric or background contributions were investigated. Structured illumination was applied in cross-correlation Doppler global velocimetry to reduce geometric scattering contributions in image acquisition, demonstrating the removal of background scattering biases in an FRS-similar technique. For multi-property measurements, it is shown that with only an order of magnitude estimate of Mie and geometric scattering, a range of wavenumbers termed the rejection region can be pre-defined such that molecular iodine absorbs the contamination. At the same time, Rayleigh scattered light can pass through. Mie and geometric scattering contributions are reduced to negligible levels within the rejection region, allowing for unbiased temperature and density measurement. Additionally, a method for determining only Doppler shift, desirable due to its increased processing speed and spatial resolution, was developed and shown to be robust to at least one order of magnitude greater Mie and geometric scattering than other methods. The biases associated with sampling a statistical average of the flow using time-averaged FRS were also investigated. The result is that measuring flow properties with the "constant in time" assumption is valid up to a turbulent intensity of 20%, resulting in biases in velocity and temperature greater than 10% of the measurement uncertainties predicted without these contributions. These advancements allow researchers to optimize measurement parameters and predict uncertainties before integrating them into a facility. These methods were implemented in a turbulent, highly distorted internal flow environment with Mie and background scattering present. Measurement uncertainties for vector velocity components, static temperature, and static density are predetermined using a 95% confidence interval on the Monte Carlo simulation results. Derived measurement uncertainties are calculated by propagating the results of the Monte-Carlo simulation. Measurements are compared to reference five-hole probe and particle image velocimetry measurements to assess the validity of the predicted uncertainty bounds. The results from this study show good agreement in the measurement of axial velocity and derived circumferential and radial flow angles when compared to reference measurements. These comparisons typically yield measurements that measure the same value as the five-hole probe data within the pre-defined uncertainty bounds of 9 m/s, 1.0°, and 3.8°, with significant deviations occurring at radii greater than 71% for tangential flow angle and radii greater than 55% for radial flow angle. Compared to facility average measurements, static density and static pressure data collected over the entire plane show RMSD values comparable to predicted measurement uncertainties of 0.043 kg/m^3 and 4.0 kPa, respectively. For the same comparison, temperature measurements show a greater RMSD than the predicted uncertainty of 8.4 K. While additional work remains to identify sources of bias error in some measurements, this work lays the foundation for FRS-based diagnostics to be used as a replacement or supplemental measurement technique in quantifying the state of fluid flow fields. / Doctor of Philosophy / Rayleigh scattering is a process that results from the interaction of light with microscopic particles that, whether we know it or not, we experience every day. When sunlight interacts with air molecules, the light scattered to our eyes is blue. The fact that the sky appears blue indicates a key property of Rayleigh scattering in that it is most efficient for the shortest wavelengths. What isn't apparent is that a whole host of other properties can be extracted from observed scattering by imaging it with a camera and a specialized filter when illuminated by a narrow wavelength laser. The problem is that a few dust particles, small enough to pass through a household air filter, can scatter more light than all the air molecules in a shot glass, with laser light scattering off large surfaces even more intense. The primary focus of this dissertation is to define Foundational approaches for realizing practical, non-intrusive filtered Rayleigh scattering techniques and methods necessary so that the light scattered from air molecules can be measured while avoiding the scattering from particles and surfaces. These approaches enable the measurement of the three-component velocity, temperature, and density of the gas being illuminated without the measurement affecting the flow itself. Because all these properties can be measured simultaneously, Rayleigh scattering provides one of the most comprehensive experimental measurement techniques available to researchers, making it highly desirable in quantifying gaseous flows and validating computational fluid dynamics calculations. Measurements collected with the techniques outlined in this work are validated experimentally using reference measurements in a large-scale internal flow facility, providing the groundwork for future applications of Rayleigh scattering-based diagnostics.