Acoustic instabilities remain a key design concern faced in the development of liquid rocket engines. The interaction between the acoustic modes and the occurring combustion reactions can be detrimental to the engine. The fluctuating pressure waves resulting from the flame oscillations in the system can potentially lead to engine failure. For this reason, research in acoustic instabilities and methods to minimize the influences on the engine, has maintain interest in the aerospace community. The scope of this study was to design, optimize and characterize acoustic behaviors of a scaled rocket combustion chamber simulating acoustic pressure waves. Tangential and longitudinal acoustic waves of the system were extracted and validated through analytical and computational fluids dynamics models. The results of this study will assist with the process of extracting dominant oscillation frequencies of a system essential in the design of acoustic suppression devices for attenuation of critical frequencies.

In recent years, hydrogen-carrying compounds have accrued interest as an alternative to traditional fossil fuels due to their function as zero-emission fuels. As such, there is interest in investigating hydrogen-carrying compounds to improve understanding of the fuels' characteristics for use in high pressure systems. In the current study, the oxidation of ammonia/natural gas/hydrogen mixtures was carried out to study CO formation profiles as well as the ignition delay times behind reflected shock waves in order to refine chemical kinetic models. Experiments were carried out in the University of Central Florida's shock tube facility by utilizing chemiluminescence to obtain OH* emission and laser absorption spectroscopy to obtain CO profiles over a temperature range between 1200 K to 1800 K with an average pressure of 2.2 atm. Experimental mixtures included both neat and combination natural gas/hydrogen with ammonia addition, with all mixtures except one having an equivalence ratio of 1. Results were then compared with the GRI 3.0 mechanism, as well as the newly developed UCF 2022 mechanism utilizing CHEMKIN-Pro software. In general, both models were able to capture the trend in autoignition delay times and CO time histories for natural gas and ammonia mixtures. However, for ammonia-hydrogen mixtures, GRI 3.0 failed to predict ignition delay times, whereas the UCF 2022 mechanism was able to capture the IDTs within the uncertainty limits of the experiments. A sensitivity analysis was conducted for different mixtures to understand the important reactions at the experimental conditions. Finally, a reaction pathway analysis was carried out to understand important ammonia decomposition pathways in the presence of hydrogen and natural gas.

Experimentally obtained droplet breakup patterns are presented for RP-2 liquid fuel droplets in the environment behind a detonation wave. To the best of our knowledge, this data is the first of its kind to examine the fundamental interactions between detonation waves and an individual fuel droplet. The experiments presented here are expected to support the ongoing effort of creating accurate models of droplet breakup in a variety of environments, which in turn will lead to enhanced predictions of rotating detonation engine performance, improved safety considerations for facilities operating in hazardous conditions, and new knowledge in energetics, hypersonics, and explosion dynamics research. Detonations were produced inside a detonation tube using a gaseous mixture of hydrogen and oxygen while the fuel droplets were allowed to fall into the line-of-sight of a pair of windows used for high-speed shadowgraphy. Baseline conditions for the detonation include an initial temperature of 293 K, an initial pressure of 760 torr, and an equivalence ratio of 0.7. Conditions produced by the detonation wave include an estimated Weber number of 150,000 and a Mach number of 0.84 for droplets with an average diameter of 2.30 mm. Comparisons are made between the observed deformation of the droplet and the results of other experiments from the literature. Comparisons of droplet deformation are also made to predictions from the Taylor Analogy Breakup model. Attempts are made to characterize the effects of different parameters, including initial pressure, equivalence ratio, the introduction of diluents to the gaseous mixture, and droplet diameter. Furthermore, the breakup of water droplets in the same baseline conditions and the breakup of fuel droplets in a methane-oxygen detonation environment are also presented for comparison.

A new shock tube test section has been designed and manufactured for the purpose of increasing the test time and expanding the applications of the shock tube for a multitude of ongoing and future projects. One purpose for the test section extension is to allow for flow visualization of droplets impacted by a shock wave for the interaction of hypersonic vehicles and atmospheric disturbances. Another purpose is to measure behind the incident shock to capture the chemical kinetics for a high-altitude environment and low-pressure, high-temperature space applications. This new test section contains 24 round optical ports for laser spectroscopy for multiple measurement locations in addition to 3 rectangular ports upstream for introducing and imaging droplets in the tube. StanShock was used to simulate the expected test time for the desired temperatures and pressures. This was compared against theoretical calculations of test time as a function of distance and velocity of the shock. The optimal length of the extension of 5 feet was then determined based on minimum required test time and limitations of the physical lab space.

The leading-edge tubercle is a type of airfoil modification that inspired by the humpback whale. It was found that the aerodynamic performance of the wing would increase compared to the wing without tubercles. In the past several years, a lot of numerical and experimental studies have been accomplished to explore this leading-edge modification. Besides the aerodynamic performance change, this research explores the aeroacoustics behavior of airfoils with leading-edge tubercles. A numerical study based on Computational Fluid Dynamics (CFD) is established, and simulations using Star CCM are accomplished based on reasonable set-ups. The airfoil chosen to create the wing is NACA 4412 which is an asymmetric airfoil. Two different tubercle wavelengths were used: 20 mm and 25 mm. The baseline airfoil is the wing that made of the same airfoil but without any modifications. For wings with leading-edge tubercles, the wavelength of the tubercles is the only changing parameter. It was found that the wings with leading-edge tubercles can reduce the noise generation, and the best noise reduction is achieved for a value of 2.525 dB (Decibel) at Point Receiver 10 for the wing that has 25 mm wavelength leading-edge tubercles. However, the wavelength of tubercles does not affect the aeroacoustics performance in an obvious way.

This study on flow-induced vibration provides valuable insights into the fundamental dynamics of fluid-structure interactions. The findings contribute to the development of predictive models and design guidelines for engineering systems susceptible to flow-induced vibration. By improving our understanding of this phenomenon, engineers can enhance the safety and reliability of various structures subjected to fluid flow, such as pipelines, flexhoses, and bellows. Flowinduced vibration is a phenomenon that occurs when fluid flow interacts with a structure, leading to oscillations and potentially causing mechanical damage. Understanding the underlying mechanisms and predicting the vibration characteristics is crucial for the design and safe operation of various engineering systems. This study presents an experimental and numerical investigation of flow-induced vibration, focusing on the effects of flow velocity, geometry, and material properties on vibration behavior. The experimental setup consists of a test rig comprising a closed-loop flow circuit and flow bench. The rig allows for adjustment of flow rate and observation of vibration responses using accelerometer sensors. Different geometric configurations and materials are considered to evaluate their influence on vibration characteristics. Primarily a series of stainless steel corrugated flexhoses following a curved flow path with a bend angle between 0 to 90 degrees and up to 3 inches in diameter were tested. A numerical study comparison is performed using two way coupled fluid-structure interface between fluid medium and flexhose convolutes. The numerical model uses commercial software to solve the continuum mechanics equations of the fluid control volume coupled with a structure finite element to solve the interactions of fluid-structure interface. The data collected includes extraction of vibration amplitudes and frequencies via a Fast Fourier Transform method with respect to the flow velocity. Results indicate a strong correlation between flow velocity and vibration amplitudes as well as increased bend angles leading to earlier flow-induced vibration event. Different geometries exhibit varying vibration patterns, highlighting the importance of structure design in mitigating flow-induced vibration. Furthermore, the material properties of the structure demonstrate significant effects on vibration behavior, suggesting the need for tailored material selection for specific applications.

Lift generating technologies are often considered a potential solution to increased power generation and reliability within wind turbine design. The Sprayed Liquid Flap (SLF) is a novel active control method that has shown success in providing lift generation on aircraft wings, but its application in the context of rotating flows is unexplored. This research aims to understand the effects of the SLF on a wind turbine and provide a pathway for future exploration of its aerodynamic impacts on rotating flows. Computational Fluid Dynamics with an Euler-Euler multiphase approach is employed to assess the influence of the SLF on a wind turbine's power generation capabilities. With the need for multiphase physics comes increased computational cost which poses a challenge for future research into the rotational multiphase flows. The Blade Element Momentum Method (BEM) provides an elegant, proven solution for estimating rotating flows for cheap so to aid in future works, the efficacy of BEM as an estimator for multiphase rotating flows will be explored through a SLF equipped wind turbine. The current findings indicate that the SLF equipped wind turbine exhibits power benefits over a conventional turbine. In addition, they suggest that BEM could serve as a reasonable estimator for the exploration of rotational multiphase physics.

Ignition systems within scramjet combust ors remain a trending topic of research because of the essential role they play in the engine's operation. An alternative to currently researched ignition systems is investigated in this study with the main goal of u tilizing the same liquid fuel as the mai n combustion chamber for the ignition system itself. In this case, JetA fuel was injected in a liquid jet in crossflow configuration with air to atomize the fuel. To characterize this ignition system, metrics such as combustion chamber pressure rise, pulse frequency, and jet penetration were used to validate possible utilization within a scramjet combustor. Tests were completed at different air temperatures ranging from 150C to 275C, varying spark plug frequencies, and at two unique combustion chamber exi t diameters. Schlieren imaging was also used to compare effects of temperature and exit nozzle diameter on jet quality. Results obtained demonstrate a high pressure rise, reliable ignition, and a fine jet exhaust fro m the combustion chamber. To increase pu lse frequency a more optimized combustion chamber is required along with a fuel injection system that would atomize the liquid fuel better than the current system. Following studies include further testing within a s upersonic flow regime to simulate the fl ow effects experienced within a scramjet combustion chamber. If results continue to prove useful , the current technology studied has the ability to innovate supersonic combustion engines by reducing mass from the flight vehicle and increasing reliability, both critical parameters.

This study investigates the utilization of computational fluid dynamics (CFD) to simulate aerodynamic heating effects in support of research and design endeavors. The initial investigation demonstrates the effectiveness of a computational approach in analyzing different geometries and flow conditions. Specifically, CFD is employed to analyze the aerodynamics of a blunt cone, double cone, and hypersonic leading edge experiencing a changing heat source across the flow/body boundary. At the stagnation point, maximum thermal loading occurs as previously found; therefore, boundary layer thickness and shock standoff distance is measured at that position to compare the results of each case. Characteristics such as temperature and pressure reveal shock and boundary layer distance and how the heat flux shifts the layers away from the body as its added into flow, and narrows the regions as the flow is cooled. For the more complex geometry of the double cone, two shocks are seen in adiabatic flow, but increasing heat flux into the flow pushes the shock layer further from the body until the shocks merge, causing drag reduction across the body; simulating an ablative heat shield that is burning. Overall, designs of a simpler nature are less influenced by heat flux, but more complex designs and regions demand considering heat flux, or even use it to an aerodynamic design advantage.

Characterizing temperature fields and species evolution inside explosive fireballs is crucial for providing constraints for model refinement and extending the current understanding of detonation afterburn chemistry. Nitromethane is of interest due to its wide variety of automotive, industrial, and military applications, including as a propellant for rockets. This effort looked to provide accurate characterization of temperature and species evolution inside of a fireball using laser absorption spectroscopy techniques. Recent advances in laser absorption spectroscopy are leveraged to make MHz-rate measurements of temperature and species concentration following the detonation of nitromethane in a controlled environment. A Fixed-Wavelength Tunable Diode Laser Absorption Spectrometer (FW-TDLAS) was developed and characterized before being interfaced with the AFRL's detonation afterburn test facility. Laser diagnostics offer many advantages over traditional measurements techniques such as being non-intrusive and allowing for time-resolved measurements of temperature and multiple species. H2O was targeted at two wavelengths in the mid-infrared to quantify the localized temporal evolution of species and temperature inside the fireball and afterburn of nitromethane. Additional diagnostics were added to allow for CO species evolution to be targeted and resolved as well.