Previous research has identified a potential link between microgravity conditions and the onset of osteoporosis, a connection that stems from altered fluidic pathways crucial in nutrient dispersion and cell stimulation. Specifically, the absence of mechanical loading in space environments reduces fluid shear stress, thereby disrupting the normal flow of interstitial fluid in trabecular bone. This disruption greatly impacts the functionality of osteoblasts and osteoclasts, the vital cells responsible for maintaining healthy bones. The focus of this study aims to explore the impact of microgravity on bone loss in astronauts, establishing the connection between the lack of mechanical loading and the reduction of fluid shear stress. Computational Fluid Dynamics (CFD) techniques are used to analyze the behavior of the interstitial fluid in the trabecular bone and the transportation of nutrients in the trabecular system. Key parameters, such as permeability and wall shear stress were examined to understand their influence on nutrient distribution. Results indicate a considerable reduction in wall shear stress in both healthy and osteoporotic bones under microgravity conditions. Higher wall shear stresses are observed in healthy bones under normal gravitational conditions, solidifying the connection between cellular stimulation and the development of osteoporosis. Additionally, a Peclet number was computed using experimental data to simulate the characteristics of interstitial fluid, indicating a significant reliance on mechanically driven flow for nutrient dispersion. The current observations not only provide valuable insights into the physiological transformations astronauts undergo in space, but also highlight the potential of CFD techniques as a powerful tool for modeling complex fluid flow within trabecular bone, paving the way for diverse biological applications.

Ignition delay times from undiluted mixtures of natural gas (NG)/H2/Air and NG/NH3/Air were measured using a high-pressure shock tube at the University of Central Florida. The combustion temperatures were experimentally tested between 1000-1500 K near a constant pressure of 25 bar. Mixtures were kept undiluted to replicate the same chemistry pathways seen in gas turbine combustion chambers. Recorded combustion pressures exceeded 200 bar due to the large energy release, hence why these were performed at the high-pressure shock tube facility. The data is compared to the predictions of the NUIGMech 1.1 mechanism for chemical kinetic model validation and refinement. An exceptional agreement was shown for stoichiometric conditions in all cases but strayed at lean and rich equivalence ratios, especially in the lower temperature regime of H2 addition and all temperature ranges of the baseline NG mixture. Hydrogen addition also decreased ignition delay times by nearly 90%, while NH3 fuel addition made no noticeable difference in ignition delay time. NG/NH3 exhibited similar chemistry to pure NG under the same conditions, which is shown in a sensitivity analysis, demonstrating hydrogen chemistry to be dominant in NG/H2 mixtures and hydrocarbon chemistry to be dominant in NG/NH3 mixtures. The reaction CH3 + O2 = CH3O + O is identified and suggested as a possible modification target to improve model performance. Increasing the robustness of chemical kinetic models via experimental validation will directly aid in designing next-generation combustion chambers for use in gas turbines, which in turn will greatly lower global emissions and reduce greenhouse effects.

There is a growing need for a fundamental understanding of how detonations are formed and sustained as propulsion technology advances toward the use of detonation-based engines. The deflagration-to-detonation transition (DDT) phenomenon is studied to better understand both the fundamentals of detonation physics and the conditions surrounding how detonations are formed and sustained. This research aims to study the effects of a wedge on DDT and detonation formation. A hydrogen-air mixture is pumped into a chamber and ignited by a spark plug. Turbulence-driven flame acceleration is induced by turbulators in the chamber through which the flame propagates. The flame then flows over and interacts with a wedge in a test section, which has quartz windows for viewing. Schlieren and chemiluminescence imaging are used to collect data from the test section. The contact of the wedge with the reacting flow creates reflected shocks that interact with and accelerate the flame front. It is also shown that DDT is repeatedly induced across from the wedge.

Initial results, design considerations, and experimental validation of a new detonation tube are presented to further improve detonation wave interaction research. The new structure consists of four independent portions: the deflagration to detonation initiation section, transition expansion section, operating test section, and dump section. The initiation, transition, and test sections are designed to operate within a temperature limit of 150°C and a maximum detonation pressure of 100 bar. The test section is comprised of interchangeable 155 cm stainless steel 316 plates assembled to create a 10x10 cm square hollow structure, sealed with longitudinal O-rings between plates and lateral O-rings between flanges and plate-ends. Ports and windows are all sealed with O-rings. The current assembly has 30 circular ports for pressure measurements and ion gauge measurements. These same circular ports will also be used for laser spectroscopy measurements through 1.27 cm diameter circular windows. Two axial rectangular windows of 16.51 x 5.74 cm and two of 16.51 x 2.54 cm, with centers 52 cm from the downstream end of the test section, are used for various diagnostics and imaging techniques. Initial detonations are validated in comparison to the literature, the facility's first detonation tube, and Chapman Jouguet conditions. 2-3 mm Rp-2 droplet breakups are also provided in comparison to the facility's first detonation tube. Introduction occurs through one of these rectangular openings where various observational tools are used to trigger the mixture's ignition when the droplet is midflight.

Particle Image Velocimetry (PIV) is an optical technique used for the visualization of fluid flow. PIV can be combined with other techniques to enhance the analysis of fluid flow. A novel far-field plasmonic resonance enhanced nanoparticle-seeded Particle Image Velocimetry (nPIV) has been demonstrated to measure the velocity in a micro channel. Chemically synthesized silver nanoparticles have been used to seed the flow. By using Discrete Dipole Approximation (DDA), plasmonic resonance enhanced light scattering has been calculated for spherical silver nanoparticles with diameters ranging from 15 nm to 200 nm in two media: water and air. The diffraction-limited plasmonic resonance enhanced images of silver nanoparticles at different diameters have been recorded. By using standard PIV techniques, the velocity within the micro channel has been determined from the images collected. The plasmonic resonance effects of nanoparticles from different media as compared to metal nanoparticles are also examined. Localized Surface Plasmon Resonance (LSPR) effects by naturally occurring Chinese yam particles are observed and quantified. Chinese yam particles are found by an atomic force microscope and a high-speed optical dark-field microscope. The particles with diameters greater than 200 nm are found to contribute most to UV-Vis absorption. LSPR effects of silver nanoparticles by the Chinese yam particles lead to the red shift of the extinction peaks of the silver nanoparticles. The wavelength shifts are quantitatively predicted based on DDA of the LSPR effects, which are sensitive to the local dielectric constant changed by the Chinese yam particles. This finding may open a new avenue to detect the biological sub-micron particles or virus in solution. PIV gives a new perspective on fluid flow that is otherwise difficult to see. An application of PIV studying the flagella movement of Giardia Lamblis trophozoites is examined. Standard PIV techniques are employed using a combination of high-contrast CytoViva ® imaging system to capture the images at high speeds and the Insight 3G software to measure the speed and direction of fluid motion generated by the microscale flagella. The PIV images illustrate how the flagella of the Giardia interact with each other and how they move in their environment.

This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.

Energy demand is expected to grow by 20% over the next 10 years. In order to account for this increase in energy consumption new and novel combustion techniques are required to mitigate the effects of pollution and fossil fuel dependency. Oxy-fuel combustion in supercritical carbon dioxide (sCO2) cycles can increase plant efficiencies up to 52% and reduce pollutants such as NOX and CO2 by 99%. Supercritical engine cycles have demonstrated electricity costs of $121/MWh, which is competitive in comparison to conventional coal ($95.60/MWh) and natural gas power plants ($128.4/MWe). This increase in efficiency is mainly driven by the near-liquid density of the working fluid (sCO2), in the super critical regime, before entering the turbine for energy extraction of the high pressure and high density sCO2 gas. In addition, supercritical CO2 engine cycles produce near-zero air emissions since CO2, a product of combustion, is the working fluid of the system which can be regenerated to the combustor. The predictive accuracy and lack of combustion models in highly CO2 diluted mixtures and at high pressures is one the major limitations to achieving optimum design of super critical engine combustors. Also, most natural gas mechanisms and validation experiments have been conducted at low pressures (typically less than 40 atm) and not in CO2 diluted environment. Thus experimental data is important for the development of modern combustion systems from work focusing on supercritical carbon dioxide cycles to rotational detonation engines. This thesis presents the design of the shock tube and two optical diagnostic techniques for measuring ignition delay times and species time histories using a shock tube in CO2 diluted mixtures.Experimental data for ignition delay times and species time-histories (CH4) were obtained in mixtures diluted with CO2. Experiments were performed behind reflected shockwaves from temperatures of 1200 to 2000 K for pressures ranging from 1 to 11 atm. Ignition times were obtained from emission and laser absorption measurements. Current experimental data were compared with the predictions of detailed chemical kinetic models (available from literature) that will allow for accurate design and modeling of combustion systems.

Ultra High Temperature Ceramic (UHTC) ZrB2- 10, 20, 30wt%SiC composites are of high interest for use in hypersonic air-breathing vehicles. In this work, ZrB2- 10, 20, 30wt%SiC UHTC composites were produced by the Spark Plasma Sintering (SPS) technique. After sintering, almost dense ceramics with ~ 5-8% porosity were produced. Their mechanical properties, such as Young’s, shear, and bulk moduli, along with Poisson’s ratio, 4-point bending strength, and single edge V-notched beam (SEVNB) fracture toughness were measured. In addition, in-situ bending experiments under a Raman microscope were performed to determine the piezo-spectroscopic coefficients of SiC Raman active peaks for calculation of thermal residual stresses. The results show that these materials are possible candidates for hypersonic airbreathing vehicles due to their high Young’s modulus, ability to withstand high temperatures, and relatively low densities.

The objective of this thesis was to develop an experimental method to research circulation control wings using numerical analysis. Specifically, it is of interest to perform 3D wind tunnel testing on a circulation control wing in the Cal Poly Low Speed Wind Tunnel (CPLSWT). A circulation control wing was designed and analyzed to determine the feasibility of this testing. This study relied on computational fluid dynamics (CFD) simulations as a method to predict the flow conditions that would be seen in a wind tunnel test. A CFD simulation was created of a wing model in a wind tunnel domain. Due to high computational requirements, reliable 3D CFD results were not obtained. This led to utilizing 2D CFD models to make estimations about the flow conditions that would be encountered in an experimental environment. The 2D CFD model was validated with previous experimental data on circulation control wings and was shown to accurately capture the flow physics. These 2D CFD results were used to create a set of guidelines to help improve the effectiveness of a future wind tunnel test campaign and demonstrate where further design work needs to be done. The key finding is that it is feasible to perform circulation control testing in the CPLSWT with limitations on the maximum momentum coefficient. Due to internal plenum pressures reaching 66 psi at Cμ=0.35, a limitation should be placed on experimental testing below the choked condition of at Cμ=0.15. This provides a more feasible operating range for the equipment available. The main performance parameter of the airfoil was met with CLMAX=5.01 at Cμ=0.35 which required 0.9 lb/s/m mass flow rate for the 2D model.

Planar and stereo particle image velocimetry measurements were conducted of a wing-tip vortex decaying in free-stream turbulence in order to understand the evolution of a vortex and its decay mechanism. The vortex decayed faster in the presence of turbulence. The decay of the circulation was found to be almost entirely due to a decrease in circulation of the vortex core, caused by the relative decrease in peak tangential velocity without a corresponding increase in core radius. These events were found to be connected with the stripping of core fluid from the vortex core. The increased rate of decay of the vortex in turbulence coincided with the formation of secondary vortical structures which wrapped azimuthally around the primary vortex. It was also found that regardless of the free-stream condition, the core scaled by peak tangential velocity and core radius.