Master of Science, The Ohio State University, 2020, Aero/Astro Engineering

This thesis covers the intensive research effort to elucidate the role of elevated temperature in deposition. Several experimental campaigns were conducted in this pursuit. The testing explored high temperature deposition with 0-10 micron Arizona Road Dust (ARD) with the intent of creating a yield strength model that included temperature effects and could be incorporated into the existing OSU deposition model. Experimental work was first conducted in the impulse kiln facility where small amounts of the test dust were placed on ceramic targets and rapidly exposed to temperatures between 1200K and 1500K. Trends in the packing factor confirmed the existence of two threshold values (1350K and 1425K) that could be linked to strength characteristics of the dust when exposed to high temperatures. Using the information obtained from the kiln experiments, HTDF testing was conducted between 1325K and 1525K. Exit temperatures were set at 25K intervals in this region with a constant jet velocity of 150 m/s. The capture efficiency data showed this trend with temperature and indicated a softening temperature and melting temperature of 1362K and 1512K respectively. With these critical values in hand, the Ohio State University Molten Model was created to modify yield strength with particle velocity and temperature. The model was tested using CFD and showed a good capability for capturing particle temperature effects in deposition from an impinging particle-laden jet. A subsequent test campaign was conducted to explore the effect of varying surface temperature on deposition. Hastelloy coupons with Thermal Barrier Coatings (TBCs) were subjected to a constant jet at 1600K jet and 200 m/s while being cooled via a backside impingement jet. Surface temperatures between 1455K and 1125K were impacted with 0-10 micron ARD while an IR camera monitored the surface. Coupons with higher coolant flowrates (lower surface temperature) saw significantly lower deposition rates than the higher surf (open full item for complete abstract)

Committee: Jeffrey Bons Dr. (Advisor); Randall Mathison Dr. (Committee Member) Subjects: Aerospace Engineering

Master of Science, The Ohio State University, 2023, Mechanical Engineering

Airborne particulate ingestion into modern, high temperature aeronautical turbine engines can cause damage to internal components, including total engine failure. Volcanic ash interactions with turbine engines has been well studied, and current research in the field focuses on other mineral based test dusts that more closely emulate desert sand and other natural materials. This work focuses on AFRL test dust, the product of an Air Force program to formulate a dust that will create engine deposits that are similar in chemical composition to those deposits found in engines post service. This test dust contains quartz, gypsum, dolomite, aplite and salt, common minerals found in Earth's crust. Utilizing high temperature facilities at The Ohio State University, a testing campaign was developed to seek further understanding of any chemical synergies between these five minerals in an impinging jet configuration. The base AFRL recipe was altered in order to remove individual minerals or increase the quantity of given mineral in proportion to the others in order to compare deposition characteristics in the context of chemical composition when compared to the base mixture. Removing any single mineral does not noticeably change capture efficiencies of AFRL when compared to the control mixture. Capture efficiencies were driven by temperature much more than any given chemical manipulations as it was found that increasing temperature will increase the capture efficiency. At a certain point, deposits cool to a shiny, glassy finish and are incredibly hard. At these temperatures, chemical synergies are better interpreted through the lens of amorphous silica glass networks and alkali network modifiers than the previously proposed ratio of calcium to silicon, although these concepts are related as a silica glass network is heavily modified by the presence of calcium. These alkali network modifiers will decrease the viscosity of a partially or fully molten deposit, and lower viscositie (open full item for complete abstract)

Committee: Lian Duan (Committee Member); Jeffrey Bons (Advisor) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Science, The Ohio State University, 2023, Aerospace Engineering

In this thesis there are two main studies. The first is an assessment of the role of mineral composition for Air Force Research Laboratory Test Dust (AFRL) for deposition in a realistic gas turbine engine environment. The second is an attempt to recreate Arizona Road Dust (ARD) synthetically by analyzing the chemical components of the natural dust and blending synthetic minerals together to match it. In the first study, experiments were performed on an effusion cooling test article with a coolant flow temperature of 894K and surface temperature of 1144K. Aerosolized dust with a 0-10 µm particle size distribution was delivered to the test article. The mineral recipe of AFRL was altered such that the presence of each of the five components ranged from 0% to 100%. For each of these AFRL recipe experiments several results were reported including capture efficiency, hole capture efficiency, mass flow reduction per gram, and normalized deposit height. Results are compared to a previous study of the inter-mineral synergies in an impingement cooling jet at the same temperature conditions. Despite differences in experimental facility flow geometry, overall agreement was found between the trends in deposition behavior of the dust blends. The strong deposition effects that were observed were shown to be related to adhesion forces of particles, mechanical properties, and chemical properties of the dust minerals. In the second study, X-Ray Diffraction (XRD) was performed on ARD to identify minerals present in a naturally sourced dust blend. Pure minerals were mixed in quantities that matched the XRD spectrum of ARD, and oxide content of this synthetic dust blend was shown to match the ISO standard (12103-1) to which ARD conforms. Particle size distribution was also matched to ARD (0-15 µm). Experiments were then conducted in four deposition facilities, one of which was representative of turbine hot section conditions (1500-1625K) and two were representative of internal coola (open full item for complete abstract)

Committee: Datta Gaitonde (Committee Member); Jeffrey Bons (Advisor) Subjects: Aerospace Engineering

Master of Science, The Ohio State University, 2018, Aero/Astro Engineering

The effect of particle size on particle accumulation within an effusion cooling geometry common to gas turbines was investigated experimentally and computationally. A flat plate with an effusion cooling hole array based on a gas turbine combustor liner was subjected to particulate laden flow in an accelerated deposition facility. The tests were conducted at an engine relevant plate temperature of 1118 K, coolant temperature of 950 K, and held at a constant pressure ratio of 1.03 (cavity to ambient). To elucidate the effect of particle size, six unique size distributions of Arizona Road Dust (ARD) smaller than 20 micron were introduced to the flow independently. Experiments were also conducted in which two different dust size distributions were sequentially delivered to the test article. These experiments clearly indicate that the smallest particles within the range tested accumulate within the hole creating deposit structures and blocking the effusion holes. They also indicate that larger particles within this range can have an erosive effect on the deposit structures as they build, changing the structure's morphology and blockage behavior. Computational fluid domains were developed to replicate the test article geometry before and after a test to investigate the effect that deposit structures have on deposition. Particles were introduced to these domains after reaching a steady solution and were tracked through the solution with a Lagrangian trajectory solver. The impact locations of the particles were recorded and a particle sticking model was employed to determine if the particles stick or rebound. The domain with the clean hole showed that the smallest particles impact and were prone to sticking in the area where deposits form experimentally. As the particles increase in size, the number of impacts and likelihood of sticking decreased. The domain with scoop deposit structures showed that these structures can change the particle impact trajectories influenci (open full item for complete abstract)

Committee: Jeffrey Bons PhD (Advisor); Jen-Ping Chen PhD (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, The Ohio State University, 2017, Aero/Astro Engineering

The increasing use of gas turbine engines in regions with high concentrations of particulate, along with the drive toward higher operating temperatures for efficiency, has led to increased problems associated with particle deposition. In order to make more informed decisions about component design and to predict life expectancy of components, a generalized physics-based model pf particle-surface interaction with deposition prediction is required. This work aims to inform existing physics-based models through the use of novel experimental and analysis techniques for measurement of particle coefficient of restitution data. This data, obtained for 20 different particle-temperature combinations and including information for more than 8.35 million individual rebounds, is used to identify areas in which existing models can be improved. Modifications suggested for a particular model include a velocity-dependent particle yield strength that accounts for strain hardening and strain rate effects and randomized rebound predictions to obtain data spread that matches that of experimental data. The modified model, with vastly improved predictive capabilities, is then used to determine temperature-dependent mechanical properties for several different particle compositions. The improvement in the model physics and the determination of thermally- and compositionally-dependent mechanical properties represents a significant advancement in deposition modeling and provides the foundation for further model improvement in the future.

Committee: Jeffrey Bons (Advisor); Mohammad Samimy (Committee Member); Randall Mathison (Committee Member) Subjects: Aerospace Engineering; Materials Science

PhD, University of Cincinnati, 2005, Medicine : Industrial Hygiene (Environmental Health)

Fungi are one of the indoor biocontaminants that can cause allergic symptoms and diseases. Moreover, fungal fragments are emerging as a potential allergenic airborne contaminant, but their health-related characteristics and methods for exposure assessment are poorly explored. On-site home visits were conducted in 777 homes enrolled in the Cincinnati Childhood Allergy and Air Pollution Study. The relationship between home characteristics and level of dustborne Alternaria allergen was investigated by using both concentration (µg/g) and loading (µg/m2). Home characteristics that were most strongly associated with the Alternaria allergen levels were those affecting the transport and penetration of particles from outdoors to indoors, and those related with the indoor microclimate. Visible mold was not associated with Alternaria allergen level. Allergen levels measured in concentration and loading units were associated with different home characteristics, and therefore, both of these units deserve to be included in the future studies. Airborne and dustborne allergen levels of Alternaria were examined using 48-hour air sampling. A poor correlation was found between airborne concentration and dustborne concentration/loading [R = 0.47 (Airconcentration vs. Dustconcentration) and 0.28 (Airconcentration vs. Dustloading)]. Therefore, both air and dust sampling are recommended at this time. Fungal fragments were investigated through a laboratory study including characterization of their size distribution and respiratory deposition. Fungal fragments of Stachybotrys chartarum (in the range of aerodynamic diameters of 0.03-0.79 µm) were released in 514 times larger quantities than spores (3.12-5.11 µm). The model calculation indicated that 60% of fragments that were retained in the respiratory tract were deposited in lower airways in infants. The number of deposited fragments in the bronchiolar and alveolar region was 4500-6200 times greater than that of spores in infants. Consider (open full item for complete abstract)

Committee: Dr. Tiina Reponen (Advisor) Subjects: