Browsing by Author "Frohnapfel, Dustin Joseph"

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    Experimental Investigation of Fan Rotor Response to Inlet Swirl Distortion
    Frohnapfel, Dustin Joseph (Virginia Tech, 2016-06-07)
    Next generation aircraft design focuses on highly integrated airframe/engine architectures that exploit advantages in system level efficiency and performance. One such design concept incorporates boundary layer ingestion which locates the turbofan engine inlet near enough to the lifting surface of the aircraft skin that the boundary layer is ingested and reenergized. This process reduces overall aircraft drag and associated required thrust, resulting in fuel savings and decreased emissions; however, boundary layer ingestion also creates unique challenges for the turbofan engines operating in less than optimal inlet flow conditions. The engine inlet flow profiles predicted from boundary layer ingesting aircraft architectures contain complex distortions that affect the engine operability, durability, efficiency, and performance. One component of these complex distortion profiles is off-axial secondary flow, commonly referred to as swirl. As a means to investigate the interactions of swirl distortion with turbofan engines, an experiment was designed to measure distorted flow profiles in an operating turbofan research engine. Three-dimensional flow properties were measured at discrete planes immediately upstream and immediately downstream of the fan rotor, isolating the component for analysis. Constant speed tests were conducted under clean and distorted test conditions. For clean tests, a straight cylindrical inlet duct was attached to the fan case; for distorted tests, a StreamVane swirl distortion generator was inserted into the inlet duct. The StreamVane was designed to induce a swirl distortion matching results of computation fluid dynamics models of a conceptual blended wing body aircraft at a plane upstream of the fan. The swirl distortion was then free to develop naturally within the inlet duct before being ingested by the engine. Results from the investigation revealed that the generated swirl profile developed, mixed, and dissipated in the inlet duct upstream of the fan. Measurements immediately upstream of the fan rotor leading edge revealed 50% reduction in measured flow angle magnitudes along with evidence of fanwise vortex convection when compared to the StreamVane design profile. The upstream measurements also indicated large amounts of secondary flow entered the fan rotor. Measurements immediately downstream of the fan rotor trailing edge demonstrated that the fan processed the distortion and further reduced the intensity of the swirl; however, non-uniform secondary flow persisted at this plane. The downstream measurements confirmed that off-design conditions entered the fan exit guide vanes, likely contributing to cascading performance deficiencies in downstream components and reducing the performance of the propulsor system.
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    Methodology Development and Investigation of Turbofan Engine Response to Simultaneous Inlet Total Pressure and Swirl Distortion
    Frohnapfel, Dustin Joseph (Virginia Tech, 2019-04-08)
    As a contribution to advancing turbofan engine ground test technology in support of propulsion system integration in modern conceptual aircraft, a novel inlet distortion generator (ScreenVaneTM) was invented. The device simultaneously reproduces combined inlet total pressure and swirl distortion elements in a tailored profile intended to match a defined turbofan engine inlet distortion profile. The device design methodology was intended to be sufficiently generic to be utilized in support of any arbitrary inlet distortion profile yet adequately specific to generate high-fidelity inlet distortion profile simulation. For the current investigation, a specific inlet distortion profile was defined using computational analysis of a conceptual boundary layer ingesting S-duct turbofan engine inlet. The resulting inlet distortion profile, consisting of both total pressure and swirl distortion elements, was used as the objective profile to be matched by the ScreenVane in a turbofan engine ground test facility. A ScreenVane combined inlet total pressure and swirl distortion generator was designed, computationally analyzed, and experimentally validated. The design process involved specifying a total pressure loss screen pattern and organizing a unique arrangement of swirl inducing turning vanes. Computational results indicated that the ScreenVane manufactured distortion profile matched the predicted S-duct turbofan engine inlet manufactured distortion profile with excellent agreement in pattern shape, extent, and intensity. Computational full-field total pressure recovery and swirl angle profiles matched within approximately 1% and 2.5° (RMSD), respectively. Experimental turbofan engine ground test results indicated that the ScreenVane manufactured distortion profile matched the predicted S-duct turbofan engine inlet manufactured distortion profile with excellent agreement in pattern shape, extent, and intensity. Experimental full-field total pressure recovery and swirl angle profiles matched within approximately 1.25% and 3.0° (RMSD), respectively. Following the successful reproduction of the S-duct turbofan engine inlet manufactured distortion profile, a turbofan engine response evaluation was conducted using the validated ScreenVane inlet distortion generator. Flow measurements collected at discrete planes immediately upstream and downstream of the fan rotor isolated the component for performance analysis. Based on the results of this particular engine and distortion investigation, the adiabatic fan efficiency was negligibly altered while operating with distorted inflow conditions when compared to nominal inflow conditions. Fuel flow measurements indicated that turbofan engine inlet air mass flow specific fuel consumption increased by approximately 5% in the presence of distortion. While a single, specific turbofan engine inlet distortion profile was studied in this investigation, the ScreenVane methodology, design practices, analysis approaches, manufacturing techniques, and experimental procedures are applicable to any arbitrary, realistic combined inlet total pressure and swirl distortion.