Doctor of Philosophy, The Ohio State University, 2022, Mechanical Engineering

Downsizing internal combustion engines along with turbocharging is an effective approach in reducing carbon dioxide emissions from vehicles to combat global warming. A turbocharger comprises a radial turbine driven by exhaust enthalpy flow connected on the same shaft to a centrifugal compressor that provides compressed air to the engine. Under certain engine operating conditions, the turbocharger faces challenges, however, due to instabilities encountered by its centrifugal compressor, primarily stall and surge. While stall adversely affects the compressor's aerodynamic performance and efficiency, surge, which is characterized by large amplitude pressure and flow rate fluctuations, results in drastic deterioration of compressor performance and may lead to complete mechanical failure of the turbocharger. The extremely loud noise (reaching 170 dB) generated during surge is also a major concern. To mitigate these instabilities, it is critical to analyze the flow structures involved in these processes. The present work therefore focuses on developing a thorough characterization of the turbocharger compressor flow field over its entire characteristic map (pressure ratio versus flowrate) using state-of-the-art experimental as well as computational techniques. The turbocharger bench stand at OSU-CAR allowed the isolation of the turbocharger's compressor from the complexities of the engine and provided a simplified bench-top environment for studying the compressor instabilities. The facility was modified by incorporating a stereoscopic particle image velocimetry (SPIV) system that facilitated velocity measurements at the compressor inlet. After integrating all the different components of this system including the laser, chiller, cameras, sheet optics, aerosol generator, laser controller, and timing unit, a methodology for stereoscopic calibration, image acquisition, and optimized post-processing was established. Extensive SPIV measurements were then carried out at the c (open full item for complete abstract)

Committee: Ahmet Selamet (Advisor) Subjects: Aerospace Engineering; Automotive Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2019, Aero/Astro Engineering

The purpose of the current work is to study the transient behavior of axial flow turbomachines in transonic environments. The first part is focused on the aerodynamic behavior of a coupled boundary layer ingesting inlet – distortion tolerant fan for use in next generation aircraft. The second part is focused on stall detection in transonic compressors. The reason these two are covered is that the fan and compressor of this future system would be mechanically linked. The fan behaves dynamically in the presence of a distortion and exhibits non-uniform flow downstream of the fan. An engine core, comprised of compressor stages, would have to operate in that distorted flow possibly inducing stall. Therefore, understanding the behavior of the fan and developing advanced stall detection methods are important for the successful implementation of these future systems. Part I – Aerodynamic Response of a Distortion Tolerant Fan Coupled to a Boundary Layer Ingesting Inlet Future aircraft designs are aimed at three main targets for more sustainable flight practices decreasing noise, emissions, and fuel burn. Boundary layer ingestion (BLI), as a part of aircraft's propulsion, is an innovative means of achieving improvements to all three targets. The BLI design incorporates engines integrated into the body of an aircraft. The engine ingests low momentum boundary layer flow that develops over the aircraft's surface when in operation. The advantages of such a system are reductions to weight, drag, noise, and increased propulsive efficiency over standard aircraft in service today. Experimental tests representing a blended wing body propulsor utilizing BLI were performed in NASA's 8ft by 6ft wind tunnel. These tests were aimed at obtaining the physically realizable benefits achievable for a boundary layer ingesting propulsor. The current work represents an effort to compare a simulated coupled boundary layer ingesting inlet and distortion tolerant fan with the experimental measure (open full item for complete abstract)

Committee: Jen-Ping Chen PhD (Advisor); Milind Bakhle PhD (Committee Member); Han-Wei Shen PhD (Committee Member); Datta Gaitonde PhD (Committee Member); Michael Dunn PhD (Committee Member) Subjects: Aerospace Engineering