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