A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Effect of Cooling on Hypersonic Boundary-Layer Stability(2022) Paquin, Laura; Laurence, Stuart J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The prediction of boundary-layer transition on hypersonic vehicles has long been considered a primary design concern due to extreme levels of heating and dynamic pressure loading this transition induces. While it has been predicted that the temperature gradient between the vehicle and the local freestream can drastically alter boundary-layer stability, experimental research on the topic over the past fifty years has provided conflicting results. This study investigates the relationship between the wall-to-edge temperature ratio and boundary-layer stability on a slender cone. Campaigns in two wind-tunnel facilities were conducted: one set within the HyperTERP reflected-shock tunnel at the University of Maryland, and one set at the high-enthalpy T5 reflected-shock tunnel at the California Institute of Technology. Both sets of campaigns employed non-intrusive, optical diagnostics to analyze the structures and spectral content within the boundary layer. In the first part of the study, performed in HyperTERP, an experimental methodology was developed to vary the wall temperature of the model using active cooling and passive thermal management. This allowed the wall temperature ratio to be varied at the same nominal test condition (and thus freestream disturbance environment), and three thermal conditions were established for analysis. Simultaneous schlieren and temperature-sensitive-paint (TSP) imaging were performed. Calibrated schlieren images quantified the unsteady density gradients associated with second-mode instabilities, and TSP contours provided insight into the thermal footprint of mean boundary-layer structures. It was found that, overall, cooling shrunk the boundary-layer thickness, increased second-mode disturbance frequencies, and increased the amplification rate of these instabilities. At nonzero angles of attack, cooling appeared to increase the azimuthal extent of flow separation on the leeward side of the cone. In the second part of the study, performed in T5, the disturbance structures and spectral content of laminar and transitional boundary layers were characterized under high-enthalpy conditions. Schlieren images indicated that, at these extremely low wall-to-edge temperature ratios, second-mode waves were confined very close to the wall in the laminar case. During the breakdown to turbulence, structures radiating out of the boundary layer and into the freestream were discovered. A texture-based methodology was used to characterize the Mach angles associated with these structures, and a wall-normal spectral analysis indicated a potential mechanism by which energy was transferred from the near-wall region to the freestream. The study presents some of the first simultaneous imaging of the flow structures and associated thermal footprint of boundary-layer transition within an impulse facility. The work also presents the first time-resolved, full-field visualizations of the second-mode dominated breakdown to turbulence at high enthalpy. Thus, the study imparts significant insight into the mechanics of boundary-layer transition at conditions representative of true hypervelocity flight.Item Dynamic Force Measurement in Hypersonic Wind Tunnels(2019) Draper III, John Willis; Lee, Sung W; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation, dynamic force measurement methodologies are developed and implemented for use in hypersonic wind tunnel testing. The chief application is implementation into Arnold Engineering Development Complex's Hypervelocity Wind Tunnel No. 9. The Sum of Weighted Accelerations Technique, Time Domain Deconvolution Method, and Frequency Domain Inverse Method are of particular interest for this study due to their implementation feasibility within Tunnel 9. The formulation of each "conventional" method is presented in its most basic or commonly used form. Then several modifications are made to improve the results of the various methods. Much of this work focuses on the specific alterations performed on each method and the consequences of each change. To improve the Sum of Weighted Accelerations Technique, modal separation and a damping matrix are added to the formulation. This allows for higher frequency accuracy and successful reconstructions on highly damped setups. A novel Time Domain Deconvolution Method is formulated in this dissertation which exhibits several advantages over the typical time domain approaches. Examples include elimination of inversion regularization, smooth reconstructions, and improved computational efficiency via response segmentation. The Frequency Domain Inverse Method was reformulated to solve directly for the frequency response function. This direct solution also allows for the use of multiple calibration tests during solution which improves accuracy. Each alteration is validated on numerical, bench top, and wind tunnel systems to provide a full theory to implementation understanding. Linked spring-mass-damper models are used for all of the numerical investigations with additive Gaussian noise and are used to draw early conclusions about each method and alteration. Bench top studies are performed on three separate support structures to build confidence in the methods on a more complex, experimental system. Finally, data obtained by tests performed in a transonic wind tunnel are used to demonstrate the capabilities and highlight some of the advantages of each method.Item Simulation of Dual-Mode Scramjet Under Thermally Choked vs. Supersonic Combustion Mode(2014) Butcher, Cameron; Yu, Kenneth H; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Effects of combustion mode and cavity flame-holder on dual-mode scramjet performance were investigated using a two-dimensional computational framework developed from commercial finite element software. The objectives were to simulate the experimental data from a laboratory model scramjet with mixing enhancement device, provide better understanding of the physical processes, and to analyze the quantitative effects on the potential performance. The isolator flow field was modeled separately to match the experimentally obtained pressure rise during the Mach 2.1 isolator entry condition. The combustor heat release distribution was systematically adjusted to reproduce the wall pressure distributions from the experiments. Case studies were conducted with and without the presence of the wall cavity for scramjet operation under both thermally-choked and supersonic-combustion mode. The combustion mode affected potential tradeoffs between thrust increase and higher thermal protection need. The presence of the cavity dampened the extent of the tradeoffs by reducing the temperature change.Item Characterization of Transient Pressure Loads in the Reservoir of a Hypersonic Blowdown Tunnel(2005-05-03) Smith, Kerrie Anne; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)When flow through a hypersonic blowdown tunnel is initiated by the bursting of a diaphragm, expansion of the process gas into the downstream vacuum of the facility creates a strong rarefaction wave. This rarefaction propagates upstream, generating significant pressure drops in upstream components, such as a heater. These pressure drops can be attenuated with the use of a metering orifice, which requires an accurate prediction of the pressure drop for proper sizing. So as to be generally applicable and to provide physical insight, a closed-form or simple numerical solution for determining this pressure drop is preferred over computational fluid dynamics. Three methods are investigated: acoustic reflection, flow pattern assumption, and the Method of Characteristics. By examining the three methods in conjunction, tradeoffs between complexity and physical accuracy can be analyzed. Ultimately, this study shall lead to the design of an experiment to verify the accuracy of the three methods.