Browsing by Subject "Aerodynamics"

Now showing 1 - 3 of 3
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    Aero-Thermal Aspects of Endwall Cooling Flows in a Gas Turbine Nozzle Guide Vane
    (2019-01) Alqefl, Mahmood
    Gas turbine engines are still one of the favorite sources for shaft power. They are relatively clean and higher in efficiency than other common sources, and their working principle makes them especially practical for aircraft propulsion. Over the past decades, the desire for higher turbine inlet temperature has increased to achieve higher specific power and efficiency. Currently, the temperature of the gasses entering the turbine is typically higher than the melting point of its components. This leads to the need of effective turbine cooling. Endwalls are particularly challenging to cool due to the complex system of secondary flows near its surface that washes the protective film coolant into the mainstream. This three-dimensional aerodynamics is also a source for irreversibility. Due to the nature of film coolant injection, its interaction with endwall aerodynamics is coupled. The film coolant momentum affects the secondary flow formation, and the secondary flows affect the film coolant distribution over the endwall. To achieve better endwall designs and cooling schemes, better understanding of this interaction is needed. This thesis studies experimentally the aero-thermal interaction of cooling flows near the endwall of a first stage nozzle guide vane passage. The test section involves engine representative combustor-turbine interface geometry, combustor coolant, and endwall film cooling flows injected upstream of a linear cascade. The approach flow conditions represent flow exiting a low NOx combustor. The aero-thermal interaction is studied through detailed measurements of passage velocity fields, thermal fields and endwall adiabatic effectiveness for various film cooling mass flow to mainstream flow ratio (MFR). The contribution of combustor coolant towards cooling the endwall is also presented. The detailed measurements revealed a new dominant vortex in the passage that is opposing the passage vortex. This vortex dominates the coolant mixing and migration and completely changes our understanding of the system of secondary flows present in a film cooled nozzle guide vane passage.
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    Dynamics and Stability of Capsules in Pipeline Transportation
    (Minnesota Department of Transportation, 1996-05) Zhao, Yiyuan; Lundgren, Thomas S.
    This project studies a new system concept for freight transportation. The idea is to use capsules to transport cargos in concealed pipelines powered by linear electric motors. Such a concept advocates the separation of freight transportation from human movement and can be very effective in reducing the ever-increasing highway congestion problem. This report examines the technical aspects of such a freight pipeline system powered by linear induction motors. Forces acting on a capsule are first discussed, followed by the study of aerodynamic drag forces on a capsule and linear induction thrust forces. Stabilities of both a single capsule and a multiple capsule system are also discussed. These results reveal the basic characteristics of a freight pipeline system, propelled by linear induction propulsion. Various technical issues are discussed. Several related topics are recommended for future research.
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    Efficient Propulsion for Versatile Unmanned Aerial Vehicles: Studies in Mechanics and Control
    (2021-02) Henderson, Travis
    This thesis presents a control algorithm for significantly enhancing the available thrust and minimizing the required electrical power consumption of a Variable-Pitch Propulsion (VPP) system, where the VPP system is made up of a brushless DC motor and a variable-collective-pitch propeller with its own servo motor. The variable-collective-pitch propeller mechanism has received recent attention because of the mechanism’s capability to enhance thrust response bandwidth and propulsive efficiency compared to conventional Unmanned Aerial Vehicle (UAV) propulsion systems with rigid-geometry propellers; the mechanism has this capability due to a second mechanical degree of freedom in the propeller geometry, allowing the collective pitch angle of the propeller blades to vary according to actuation from a servo motor. When paired with a properly designed control algorithm, the motor speed and pitch angle can be tuned in real time to track prescribed thrust trajectories while satisfying some optimality condition. Motivation for research into highly efficient VPP propulsion systems is encouraged by the intense interest from private and public sectors in UAVs that are capable of Vertical TakeOff and Landing (VTOL); while generally capable of both fixed-wing and hovering flight, VTOL UAVs with rigid-geometry propellers often exhibit short flight time due to non-optimal propulsion system efficiency across-the-board. Prior research into power-minimizing control strategies for small VPP systems has been targeted at multi-rotor platforms and has thus made assumptions that limit variation in the speed of propeller inflow and in the magnitude of thrust, thus limiting the technology’s applicability to VTOL platforms. The control algorithm presented in this thesis is designed to accommodate for the wide range of air inflow speeds and thrust magnitudes through the following algorithm components: a linear feedback thrust controller with a nonlinear, adaptive feedforward thrust model derived from Blade Element Momentum propeller theory; an estimator to tune the thrust feedforward model parameters in real-time; and an Extremum Seeking algorithm for tracking the minimum-power control input configuration. Analysis of controller performance is discussed with reference to simulated and physical validation experiments.