Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Heat Transfer Measurements in a Supersonic Film Flow(2016) Adamson, Colin Sawyer; Cadou, Christopher; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents measurements of wall heat flux and flow structure in a canonical film cooling configuration with Mach 2.3 core flow in which the coolant is injected parallel to the wall through a two-dimensional louver. Four operating conditions are investigated: no film (i.e. flow over a rearward-facing step), subsonic film, pressure-matched film, and supersonic film. The overall objective is to provide a set of experimental data with well characterized boundary conditions that can be used for code validation. The results are compared to RANS and LES simulations which overpredict heat transfer in the subsonic film cases and underpredict heat transfer in supersonic cases after film breakdown. The thesis also describes a number of improvements that were made to the experimental facility including new Schlieren optics, a better film heater, more data at more locations, and a verification of the heat flux measurement hardware and data reduction methods.Item Slot Film Cooling: A Comprehensive Experimental Characterization(2016) Raffan Montoya, Fernando; Marshall, Andre W; Cadou, Christopher; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)When components of a propulsion system are exposed to elevated flow temperatures there is a risk for catastrophic failure if the components are not properly protected from the thermal loads. Among several strategies, slot film cooling is one of the most commonly used, yet poorly understood active cooling techniques. Tangential injection of a relatively cool fluid layer protects the surface(s) in question, but the turbulent mixing between the hot mainstream and cooler film along with the presence of the wall presents an inherently complex problem where kinematics, thermal transport and multimodal heat transfer are coupled. Furthermore, new propulsion designs rely heavily on CFD analysis to verify their viability. These CFD models require validation of their results, and the current literature does not provide a comprehensive data set for film cooling that meets all the demands for proper validation, namely a comprehensive (kinematic, thermal and boundary condition data) data set obtained over a wide range of conditions. This body of work aims at solving the fundamental issue of validation by providing high quality comprehensive film cooling data (kinematics, thermal mixing, heat transfer). 3 distinct velocity ratios (VR=uc/u∞) are examined corresponding to wall-wake (VR~0.5), min-shear (VR ~ 1.0), and wall-jet (VR~2.0) type flows at injection, while the temperature ratio TR= T∞/Tc is approximately 1.5 for all cases. Turbulence intensities at injection are 2-4% for the mainstream (urms/u∞, vrms/u∞,), and on the order of 8-10% for the coolant (urms/uc, vrms/uc,). A special emphasis is placed on inlet characterization, since inlet data in the literature is often incomplete or is of relatively low quality for CFD development. The data reveals that min-shear injection provides the best performance, followed by the wall-jet. The wall-wake case is comparably poor in performance. The comprehensive data suggests that this relative performance is due to the mixing strength of each case, as well as the location of regions of strong mixing with respect to the wall. Kinematic and thermal data show that strong mixing occurs in the wall-jet away from the wall (y/s>1), while strong mixing in the wall-wake occurs much closer to the wall (y/s<1). Min-shear cases exhibit noticeably weaker mixing confined to about y/s=1. Additionally to these general observations, the experimental data obtained in this work is analyzed to reveal scaling laws for the inlets, near-wall scaling, detecting and characterizing coherent structures in the flow as well as to provide data reduction strategies for comparison to CFD models (RANS and LES).Item Experimental Investigation of Film Cooling in a Supersonic Environment(2015) Collett, Matthew Dane; Cadou, Christopher P; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis reports the results of an experimental investigation of film cooling in a supersonic environment using a modified version of an apparatus originally developed by Daanish Maqbool. A test matrix of conditions relevant to those found in the nozzle extension of the NASA J-2X rocket engine was used as the basis for the testing plan. A film heater was designed and constructed to enable operation at all points in the test matrix. Temperature-time histories from thermocouples embedded in the test section walls were used to compute the spatial evolution of the film cooling effectiveness at each test condition. The results were compared to numerical simulations by NASA's Loci-CHEM CFD tool. Standard speed (30 Hz) Schlieren videos of the film injection region were recorded and new machine vision-based techniques for automatically extracting flow information from Schlieren images were implemented.Item EXPERIMENTAL AND NUMERICAL INVESTIGATION OF TANGENTIALLY-INJECTED SLOT FILM COOLING(2013) Voegele, Andrew; Trouve, Arnaud; Marshall, Andre; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Film cooling is a technique used in gas turbine engines, and blades and rocket nozzles to protect critical surfaces from the hot combustion gases. In film cooling applications, a relatively cool thin fluid is injected along surfaces and subsequently mix with the hot mainstream, thus leading to a reduction of protection at the wall. The breakdown of this film involves complex physics including intense turbulent mixing, heat transfer, conduction, radiation and variable density effects to name a few. In this dissertation, film cooling is both experimentally measured and numerically simulated. The experiments feature non-intrusive Particle Image Velocimetry to provide two-dimensional planes of mean and fluctuating velocity, which are critical in order to characterize and understand the turbulent flow phenomena involved in film cooling. Additionally, through the use of micro-thermocouples, the thermal flow fields and wall temperatures are non-intrusively measured, with very small radiative errors. The film cooling flows are experimentally varied to cover a variety of breakdown regimes for both adiabatic (or idealized walls with no heat loss) and on-adiabatic walls (or walls with a carefully controlled heat loss through them). The subsequent experimental dataset is a unique and comprehensive set of turbulent measurements characterizing and demonstrating the film breakdown and the turbulent flow physics. The experiments are then numerically simulated using an in-house variable density, Large Eddy Simulation (LES) Computational Fluid Dynamics (CFD) code developed as part of this dissertation. In addition to accurately predicting important turbulent kinematic and thermal flow phenomena, the key wall parameters were predicted to within 3% for the adiabatic cases and to within 6% for the non-adiabatic cases, with a few exceptions. Turbulent inflow techniques, crucial for the success of LES of film cooling, are examined. In addition to the turbulent flow physics, radiation and conduction physics at the wall were also simulated with good fidelity. The combined experimental and numerical approach was used to uniquely form a comprehensive study, examining many aspects of film cooling phenomena relevant for engineering applications.Item Numerical Characterization and Modeling of Adiabatic Slot Film Cooling(2011) Voegele, Andrew; Marshall, André W; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Film cooling is a technique used to protect critical surfaces in combustors, thrust chambers, turbines and nozzles from hot, chemically reacting gases. Accurately predicting the film's performance is especially challenging in the vicinity of the wall and the film injection plane due to the complex interactions of two highly turbulent, shearing, boundary layer flows. Properly characterizing the streams at the inlet of a numerical simulation and the choice of turbulence model are crucial to accurately predicting the decay of the film. To address these issues, this study employs a RANS solver that is used to model a film cooled wall. Menter's baseline model, and shear-stress transport model and the Spalart-Allmaras model are employed to determine the effect on film cooling predictions. Several methods for prescribing the inlet planes are explored. These numerical studies are compared with experimental data obtained in a UMD film cooling wind tunnel.Item Experimental Characterization of Slot Film Cooling Flows With Minimally Intrusive Diagnostics(2008) Raffan, Fernando; Marshall, Andre; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The performance of a propulsion system is directly proportional to its operating temperature; therefore, an optimum operation regime will undoubtedly generate intense thermal loads on system components. If the system is designed for reusability and/or long range missions, it may be necessary to perform active cooling of critical components to prevent premature failure of the system. One such method is film cooling, in which a layer of relatively cool gas is injected near the surface to be protected. This work describes the use of minimally intrusive diagnostics to characterize the kinematics, thermal dynamics and heat transfer of slot film cooling flows over a wide range of blowing ratios, generating a comprehensive database for detailed analysis, as well as for further use by model developers.