Browsing by Subject "Structure-function"
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Item Anisotropic hybrid turbulence modeling with specific application to the simulation of pulse-actuated dynamic stall control(2015-12) Haering, Sigfried William; Moser, Robert deLancey; Murthy, Jayathi; Bogard, David G; Ezekoye, Ofodike A; Oliver, ToddExperimental studies have shown pulse actuated dynamic stall control may provide a simple means to significantly increase the performance of lifting surfaces and expand their flight envelope. However, precise information of the complex boundary layer reattachment mechanisms are inaccessible to experimental measurements. Therefore, simulations are necessary to fully understand, optimize, and apply this method. Due to the inherent shortcomings of RANS, computational expense of LES, and deficiencies in current hybrid modeling approaches, a new hybrid modeling framework has been developed. Based in using the two-point second-order structure function to drive a local equilibrium between resolved and modeled turbulence, the new approach addresses issues associated with inhomogeneous and anisotropic grids as well as the treatment of the RANS/LES interface in hybrid simulations. Numerical studies using hybrid RANS/LES modeling approaches of a stalled airfoil with spanwise-uniform actuation regions experiencing single pulse actuated flow reattachment have been performed. The mechanism responsible for reattachment has been identified as a repeating wall-vortex interaction process. The new hybrid framework and anisotropic SGS models developed here are anticipated to be of great benefit well beyond the focus of this work with application to many challenging flow situations of pressing engineering interest.Item Gold-catalyzed alcohol oxidation reactions : insights from surface science and classical catalysis studies(2016-12) Mullen, Gregory Michael; Mullins, C. B.; Henkelman, Graeme; Humphrey, Simon; Hwang, Gyeong; Korgel, BrianCatalysts play an extremely important role in shaping the world around us. Foods, plastics, fuels, medicines, and countless other materials that are integral to our way of life rely on catalysts for their production. Despite their importance, to this day catalysts are still mysterious materials with active sites and reaction mechanisms that often remain unknown despite decades of investigation. In this dissertation, we investigate the use of gold catalysts for selective oxidation of alcohols, an important class of reaction used in the agrochemical, pharmaceutical, and fine chemicals industries. Using surface science and classical catalysis techniques, we demonstrate that water plays important and previously undiscovered roles in these processes, altering reaction mechanisms and influencing the selectivity exhibited by the catalysts for primary and secondary oxidation pathways. Additionally, we show that the structure and the composition of the support material both influence the activity and selectivity of gold catalysts for alcohol oxidation. Our results highlight the complexity that catalytic reaction mechanisms can exhibit and the structure-function relationships that can dictate their behavior. Knowledge of these factors is extremely valuable optimizing the design and implementation of catalytic processes. By leveraging knowledge like this, we will be able to mitigate the generation of industrial waste make better use of our natural resources.