The use of serpentine boundary layer ingesting (BLI) diffusers offers a significant benefit to the performance of Blended Wing Body aircraft. However, the inherent diffuser geometry combined with a thick ingested boundary layer creates strong secondary flows that lead to severe flow distortion at the engine face, increasing the possibility of engine surge. This study investigated the use of enabling active flow control methods to reduce engine-face distortion. An ejector-pump based system of fluidic actuators was used to directly manage the diffuser secondary flows. This system was modeled computationally using a boundary condition jet modeling method, and tested in an ejector-driven wind tunnel facility. This facility is capable of simulating the high-altitude, high subsonic Mach number conditions representative of BWB cruise conditions, specifically a cruise Mach number of 0.85 at an altitude of 39,000 ft. The tunnel test section used for this experiment was designed, built, and tested as a validation tool for the computational methods. This process resulted in the creation of a system capable of efficiently investigating and testing the fundamental mechanisms of flow control in BLI serpentine diffusers at a minimum of time and expense. Results of the computational and wind tunnel analysis confirmed the large potential benefit of adopting fluidic actuators to control flow distortion in serpentine BLI inlets. Computational analysis showed a maximum 71% reduction in flow distortion at the engine face through the use of the Pyramid 1 ejector scheme, and a 68% reduction using the Circumferential ejector scheme. However, the flow control systems were also found to have a significant impact on flow swirl. The Pyramid 1 ejector scheme was found to increase AIP flow swirl by 64%, while the Circumferential ejector scheme reduced flow swirl by 30%. Computational analyses showed that this difference was the result of jet interaction. By keeping the jet flows separate and distinct, the diffuser secondary flows could be more efficiently managed. For this reason, the most practically effective flow control scheme was the Circumferential ejector scheme. Experimental results showed that the computational analysis slightly over-predicted flow distortion. However, the trends are accurately predicted despite slight variances in freestream Mach number between runs and a slightly lower tested altitude. / Master of Science

The military's desire for ducted fan vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs) stems from the vehicles' relatively small size, safety in tight quarters, increased payload capacity for their size, and their ability to hover for surveillance missions. However, undesirable aerodynamic characteristics are associated with these vehicles in crosswinds, namely momentum drag and asymmetric duct lift. Because the duct itself, and not the fan, is the root cause of these unfavorable aerodynamic attributes, various lip shapes were tested to determine the effects of leading edge radius of curvature and duct wall thickness. It was found that a lip with a small leading edge radius performed best in forward flight and crosswind conditions, while the performance of a lip with a large leading edge radius was enhanced in static conditions. Through tuft flow visualization and static pressure measurements it was determined that the reason for the difference in performance between the two lips was due to flow separation on the interior of the duct lip surface. Control vanes positioned aft of the duct were tested as the primary attitude control for the vehicle. An empirical control vane model was created based on the static data for the control vanes, and it was applied to wind tunnel test results to determine the required control vane angle for trim. Wind tunnel testing showed the control vanes were capable of trimming out the adverse pitching moment generated by the duct, but at some flight speeds large vane deflections were necessary. Additional control devices placed at the lip of the duct and stabilizer vanes positioned aft of the duct were tested to reduce the amount of control vane deflection required for trim. It was found that the duct deflector control effector had the largest impact on the adverse pitching moment, while the stabilizer vanes were only effective at low crosswind velocities. / Master of Science

No / There is an ongoing debate about the reasons for and factors contributing to healthcare-associated infection (HAI). Different solutions have been proposed over time to control the spread of HAI, with more focus on hand hygiene than on other aspects such as preventing the aerial dissemination of bacteria. Yet, it emerges that there is a need for a more pluralistic approach to infection control; one that reflects the complexity of the systems associated with HAI and involves multidisciplinary teams including hospital doctors, infection control nurses, microbiologists, architects, and engineers with expertise in building design and facilities management. This study reviews the knowledge base on the role that environmental contamination plays in the transmission of HAI, with the aim of raising awareness regarding infection control issues that are frequently overlooked. From the discussion presented in the study, it is clear that many unknowns persist regarding aerial dissemination of bacteria, and its control via cleaning and disinfection of the clinical environment. There is a paucity of good-quality epidemiological data, making it difficult for healthcare authorities to develop evidence-based policies. Consequently, there is a strong need for carefully designed studies to determine the impact of environmental contamination on the spread of HAI.

<p> </p> <p>ndoor air quality (IAQ) due to the presence of airborne microorganisms or bioaerosols (0.01-10 μm) in indoor spaces has been a concern for many years; however, it gained significant attention during the COVID-19 pandemic. Photocatalytic oxidation (PCO) has shown promising potential to kill microorganisms (removal/disinfection) and has already been in use within HVAC systems to treat volatile organic compounds (VOCs) (treatment). The main motivation of this work is to understand whether PCO devices can be used for bioaerosol removal in indoor spaces by integrating them with HVAC systems. Among the various factors that influence the adoption of PCO for large-scale bioaerosol removal, this work specifically tries to investigate two factors 1) whether the commercially available PCO reactors for treatment can be used for removal/disinfection or not, and 2) how to setup a standardized experimental setup for evaluating the removal efficiency of these systems. Generally, most of the commercial PCO devices use UV- based photocatalysis, so the removal efficiency is a combination of inactivation by UV and the reactive oxygen species produced by photocatalytic reactions (pure photocatalytic effect).</p> <p>In this work, the bioaerosol transport and the photon transport in a reactor is hypothesized as central to using the photocatalytic effect to inactivate microorganisms. This study uses analytical models to estimate the collection efficiency of the bioaerosols inside the honeycomb channels as a function of non-dimensional aspect ratios and velocity typical of HVAC systems. Subsequently, the collection efficiency results are overlaid with the prior literature results on photon transport inside such channels to present a limiting case for the removal efficiency of these systems. Another crucial factor for the performance of PCO systems is to investigate about the bioaerosol remediation on a photocatalyst substrate. Since there are many challenges associated with the numerical modeling of this phenomenon, this work developed a standardized experimental setup at the Herrick Laboratories, Purdue to investigate these interactions and further validate the previous hypothesis .The setup is constructed to systematically characterize the bioaerosol flowing through the airstream and measure data crucial to the PCO reactor performance, such as fluence rate field, number concentration (#/cm3), and viable concentration (CFU or PFU/m3) of the microorganisms upstream and downstream of the treatment sections. </p> <p>The collection efficiency (CE) of bioaerosols in honeycomb channels with velocities typical to HVAC systems were estimated using analytical models, and the results were presented in dimensionless aspect ratios (AR= Lch/ Dch). Based on the CE modeling results, the highest CE for aspect ratio 25 was less than 20% for the entire bioaerosol size range. From the prior literature results on photon transport, it was found that the intensity of the light reduced significantly for aspect ratios less than or equal to 6. Based on these results, it was found that the existing honeycomb geometries weren’t effective for PCO disinfection in operating conditions typical of HVAC systems. Since there aren’t any existing well-established methods to experimentally investigate these kinds of systems, this work will present the details about the development of the proposed methods inspired from prior literature for general air cleaning devices and small-scale PCO experiments. Furthermore, a detailed discussion about the important subsystems such as aerosol generation subsystem, sampling subsystem, and reactor subsystem which is crucial to investigating the hypotheses is presented in this thesis. Finally, some preliminary results on each of these characterization experiments to test the hypotheses has been presented in this thesis.</p>

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