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You searched for +publisher:"Clemson University" +contributor:("Dr. Jay Ochterbeck"). Showing records 1 – 2 of 2 total matches.

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Clemson University

1. Galgalikar, Rohan Ram. Computational Engineering Analysis of Materials and Structural Aspects of Gas Turbine Engine Ceramic Matrix Composite Components.

Degree: PhD, Mechanical Engineering, 2016, Clemson University

Ever increasing world energy need and growing environmental concerns have resulted in rising efficiency and reduced emissions requirements from the energy industry. Current gas turbines, widely used for power generation, have reached a plateau in efficiency. To further boost their efficiency and reduce emissions it is imperative to increase the operating temperatures. This necessitates the advent of new materials which have higher temperature capability than the existing super alloys, used to manufacture current gas turbines. Ceramic Matrix Composites (CMCs) are such a class of material, which have very high melting points and are extremely light weight in comparison to the superalloys. The CMCs are made from ceramic constituents that are inherently brittle; however, the CMCs show metal-like ductile behavior. The present work focuses on a non-oxide class of CMCs which are made SiC fibers and SiC matrix. A room temperature multi-length scale constitutive material model has been developed by homogenization at two characteristic microstructural Length Scales (LS), fiber/tow LS and ply/lamina LS. The results obtained from virtual mechanical tests on representative volume elements for the two LS are homogenized to generate a component length scale material model which exhibits the characteristic elastic and inelastic behavior of CMCs. This material model is implemented as a user subroutine for a commercial finite element package ABAQUS. Being a relatively new class of material, the CMCs are targeted initially for manufacturing low stress bearing stationary components in the hot-section of the gas turbines. Hence, the material model is tested by conducting a foreign object impact test on a typical stationary gas turbine hot-section component, namely the inner shroud. The effect of fiber architecture (cross-ply vs. plain weave) and strength of the fiber-matrix bond on the impact resistance of the inner shroud is demonstrated. In the hot-section of the gas turbine, the CMC components experience significant in-service high temperature environmental degradation. To capture this degradation four environmental effects: (a) grain growth and porosity growth; (b) creep; (c) dry oxidation; and (d) wet oxidation, have been identified. Using experimental data reported in open literature, the component length scale CMC material model properties are modified to be a function of the nature, duration and extent of the environmental exposure. Again, foreign object impact tests are conducted to measure the CMC material degradation after exposing it to the four environmental conditions. Out of the four environmental effects considered the wet oxidation results in highest material degradation, at a given time and temperature exposure. After the commercial success of stationary CMC components is established, more hot-section components like turbine blades are expected to be made from CMCs to further extend the efficiency benefits offered by the use of CMCs in gas turbines. Creep is a primary failure mechanism for rotating… Advisors/Committee Members: Dr. Mica Grujicic, Committee Chair, Dr. Chenning Tong, Dr. Jay Ochterbeck, Dr. Rajendra Singh.

Subjects/Keywords: Ceramic Matrix Composite; Finite Element Analysis; Gas Turbines; Multi-Length scale material modeling

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Galgalikar, R. R. (2016). Computational Engineering Analysis of Materials and Structural Aspects of Gas Turbine Engine Ceramic Matrix Composite Components. (Doctoral Dissertation). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_dissertations/1670

Chicago Manual of Style (16th Edition):

Galgalikar, Rohan Ram. “Computational Engineering Analysis of Materials and Structural Aspects of Gas Turbine Engine Ceramic Matrix Composite Components.” 2016. Doctoral Dissertation, Clemson University. Accessed January 17, 2021. https://tigerprints.clemson.edu/all_dissertations/1670.

MLA Handbook (7th Edition):

Galgalikar, Rohan Ram. “Computational Engineering Analysis of Materials and Structural Aspects of Gas Turbine Engine Ceramic Matrix Composite Components.” 2016. Web. 17 Jan 2021.

Vancouver:

Galgalikar RR. Computational Engineering Analysis of Materials and Structural Aspects of Gas Turbine Engine Ceramic Matrix Composite Components. [Internet] [Doctoral dissertation]. Clemson University; 2016. [cited 2021 Jan 17]. Available from: https://tigerprints.clemson.edu/all_dissertations/1670.

Council of Science Editors:

Galgalikar RR. Computational Engineering Analysis of Materials and Structural Aspects of Gas Turbine Engine Ceramic Matrix Composite Components. [Doctoral Dissertation]. Clemson University; 2016. Available from: https://tigerprints.clemson.edu/all_dissertations/1670

2. Li, Wei. Effects of Mean Shear and Scalar Initial Length Scale on Three-Scalar Mixing in Turbulent Coaxial Jets.

Degree: PhD, Mechanical Engineering, 2016, Clemson University

The effects of the velocity and length scale ratios of the annular flow to the center jet on three-scalar mixing in turbulent coaxial jets are investigated. In this flow a center jet and an annular flow, consisting of acetone-doped air and ethylene respec-tively, are mixed with the co-flow air. Simultaneous planar laser-induced fluorescence and Rayleigh scattering are employed to measure the mass fractions of the acetone-doped air and ethylene. The velocity ratio alters the relative mean shear rates in the mixing layers between the center jet and the annular flow and between the annular flow and the co-flow, modifying the scalar fields through mean-flow advection, turbu-lent transport, and small-scale mixing. The length scale ratio determines the degree of separation between the center jet and the co-flow. The results show that while varying the velocity ratio can alter the mixing characteristics qualitatively, varying the annulus width only has quantitative effects. Increasing the velocity ratio and the annulus width always delays the evolution of the scalar fields. The evolution of the mean scalar profiles are dominated by the mean-flow advection, while the shape of the joint probability density function (JPDF) is largely determined by the turbulent transport and molecular diffusion. The JPDF for the higher velocity ratio cases is bimodal at some locations while it is unimodal for the lower velocity ratio cases. The diffusion velocity streamlines in scalar space representing the conditional diffusion generally converge quickly to a manifold along which they continue at a lower rate. The curvature of the manifold is significantly larger for the higher velocity ratio cases. Predicting the mixing path along the manifold as well as its dependence on the velocity and length scale ratios presents a challenging test for mixing models. The three-scalar subgrid-scale (SGS) mixing in the context of large eddy simu-lation and its dependence on the velocity and length scale ratios are also investigated. The analysis reveals two SGS mixing regimes depending on the SGS variance value of the center jet scalar. For small SGS variance the scalars are well mixed with uni-modal filtered joint density function (FJDF) and the three-scalar mixing configuration is lost. For large SGS variance, the scalars are highly segregated with bimodal FJDFs at radial locations near the peak of the mean SGS variance of the center jet scalar. Two competing factors, the SGS variance and the scalar length scale, are important for the bimodal FJDF. For the higher velocity ratio cases, the peak value of the SGS variance is higher, thereby resulting in stronger bimodality. For the lower velocity ratio cases, the wider mean SGS variance profiles and the smaller scalar length scale cause bimodal FJDFs over a wider range of physical locations. The diffusion stream-lines first converge to a manifold and continue on it toward a stagnation point. The curvature of the diffusion manifold is larger for the larger velocity ratio cases. The manifold provides a SGS mixing path for the center… Advisors/Committee Members: Dr. Chenning Tong, Committee Chair, Dr. Richard Miller, Dr. Jay Ochterbeck, Dr. Xiangchun Xuan.

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Li, W. (2016). Effects of Mean Shear and Scalar Initial Length Scale on Three-Scalar Mixing in Turbulent Coaxial Jets. (Doctoral Dissertation). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_dissertations/1717

Chicago Manual of Style (16th Edition):

Li, Wei. “Effects of Mean Shear and Scalar Initial Length Scale on Three-Scalar Mixing in Turbulent Coaxial Jets.” 2016. Doctoral Dissertation, Clemson University. Accessed January 17, 2021. https://tigerprints.clemson.edu/all_dissertations/1717.

MLA Handbook (7th Edition):

Li, Wei. “Effects of Mean Shear and Scalar Initial Length Scale on Three-Scalar Mixing in Turbulent Coaxial Jets.” 2016. Web. 17 Jan 2021.

Vancouver:

Li W. Effects of Mean Shear and Scalar Initial Length Scale on Three-Scalar Mixing in Turbulent Coaxial Jets. [Internet] [Doctoral dissertation]. Clemson University; 2016. [cited 2021 Jan 17]. Available from: https://tigerprints.clemson.edu/all_dissertations/1717.

Council of Science Editors:

Li W. Effects of Mean Shear and Scalar Initial Length Scale on Three-Scalar Mixing in Turbulent Coaxial Jets. [Doctoral Dissertation]. Clemson University; 2016. Available from: https://tigerprints.clemson.edu/all_dissertations/1717

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