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Multiphase Interaction in Low Density Volumetric Charring Ablators University of Kentucky UKnowledge Theses and Dissertations--Mechanical Engineering Mechanical Engineering 2018 Multiphase Interaction in Low Density Volumetric Charring Ablators Ali D. Omidy University of Kentucky, [email protected] Digital Object Identifier: https://doi.org/10.13023/etd.2018.476 Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Omidy, Ali D., "Multiphase Interaction in Low Density Volumetric Charring Ablators" (2018). Theses and Dissertations--Mechanical Engineering. 128. https://uknowledge.uky.edu/me_etds/128 This Doctoral Dissertation is brought to you for free and open access by the Mechanical Engineering at UKnowledge. It has been accepted for inclusion in Theses and Dissertations--Mechanical Engineering by an authorized administrator of UKnowledge. For more information, please contact [email protected]. STUDENT AGREEMENT: I represent that my thesis or dissertation and abstract are my original work. Proper attribution has been given to all outside sources. I understand that I am solely responsible for obtaining any needed copyright permissions. I have obtained needed written permission statement(s) from the owner(s) of each third-party copyrighted matter to be included in my work, allowing electronic distribution (if such use is not permitted by the fair use doctrine) which will be submitted to UKnowledge as Additional File. I hereby grant to The University of Kentucky and its agents the irrevocable, non-exclusive, and royalty-free license to archive and make accessible my work in whole or in part in all forms of media, now or hereafter known. I agree that the document mentioned above may be made available immediately for worldwide access unless an embargo applies. I retain all other ownership rights to the copyright of my work. I also retain the right to use in future works (such as articles or books) all or part of my work. I understand that I am free to register the copyright to my work. REVIEW, APPROVAL AND ACCEPTANCE The document mentioned above has been reviewed and accepted by the student’s advisor, on behalf of the advisory committee, and by the Director of Graduate Studies (DGS), on behalf of the program; we verify that this is the final, approved version of the student’s thesis including all changes required by the advisory committee. The undersigned agree to abide by the statements above. Ali D. Omidy, Student Dr. Alexandre Martin, Major Professor Dr. Alexandre Martin, Director of Graduate Studies Multiphase Interaction in Low Density Volumetric Charring Ablators DISSERTATION A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Engineering at the University of Kentucky By Ali D. Omidy Lexington, Kentucky Director: Dr. Alexandre Martin, Professor of Mechanical Engineering Lexington, Kentucky 2018 Copyright© Ali D. Omidy 2018 ABSTRACT OF DISSERTATION Multiphase Interaction in Low Density Volumetric Charring Ablators The present thesis provides a description of historical and current modeling methods with recent discoveries within the ablation community. Several historical assumptions are challenged, namely the presence of water in Thermal Protection System (TPS) materials, presence of coking in TPS materials, non-uniform elemental production during pyrolysis reactions, and boundary layer gases, more specifically oxygen, inter- actions with the charred carbon interface. The first topic assess the potential effect that water has when present within the ablator by examining the temperature profile histories of the recent flight case Mars Science Laboratory. The next topic uses experimental data to consider the instanta- neous gas species produced as the ablator pyrolyzes. In this study, key gas species are identified and assumed to be unstable within the gas phase; thus, equilibrating to the solid phase. This topic investigates the potential effects due to the these process. The finial topic uses a simplified configuration to study the role of carbon oxidation, from diatomic oxygen, on the ablation modes of a TPS, surface versus volumetric ablation. Although each of these topics differ in their own right, a common theme is found by understanding the role that common pyrolysis and boundary layer gases species have as they interacts with the porous TPS structure. The main objective of the present thesis is to investigate these questions. KEYWORDS: Atmospheric Entry, Material Response, Heat Transfer Author's signature: Ali D. Omidy Date: December 6, 2018 Multiphase Interaction in Low Density Volumetric Charring Ablators By Ali D. Omidy Director of Dissertation: Alexandre Martin Director of Graduate Studies: Alexandre Martin Date: December 6, 2018 This document is dedicated to my family and fianc´e.Without each of your love and support, I would not have survived graduate school. I thank each of you from the bottom of my heart. ACKNOWLEDGMENTS I would like to express my gratitude to Dr. Alexandre Martin for serving as my Ph.D. advisor and Dr. Jos´eGra~na-Oteroas my co-advisor. Without their guidance throughout my education I would not be in the position I am today. I would like to also thank them for their friendship over the years making my time at the university much more enjoyable. I would like to extend a special thanks to Dr. Martin for taking mr in as a \young" undergraduate student. His patience and motivation during this period gave me the confidence to pursue this degree. I would also like to express a great deal of gratitude to my mentors and friends at NASA Johnson Space Center and Ames Research Center, namely Brian Remark, Cooper Snapp, Stan Bouslog, Carlos Westhelle, Alvaro Rodriguez, Scott Coughlin, Ron Lewis, Adam Amar, Brandon Oliver, Nagi Mansour, and David Hash. Each of them have made my experiences at NASA very memorable and have all taught me so much. I would like to thanks my remaining committee members Dr. Kaveh Tagavi and Dr. Brad Berron for the time and expertise throughout this process. Lastly I would like to thank my friend/lab-mates, namely, Martin, Umran, Ra- gava, Rick, Olivia, Justin, Christen, Nick, and Chris. You all have made this experi- ence memorable and enjoyable. iii TABLE OF CONTENTS Acknowledgments . iii Table of Contents . iv List of Figures . vi List of Tables . viii Chapter 1 Introduction to Atmospheric Entry . 1 1.1 Thermal protection materials . 2 1.2 Literature Review . 7 Chapter 2 Governing equations and material models . 11 2.1 Governing equations . 11 2.2 Boundary conditions . 13 2.3 Material models . 16 2.4 Effective thermal conductivity model remarks . 19 Chapter 3 Effects of water phase change on the material response of low- density carbon-phenolic ablators . 21 3.1 Mars Science Lab entry data . 21 3.2 Effect of water on the material properties of PICA . 23 3.3 Concluding remarks on effects of water phase change on the material response of low-density carbon-phenolic ablators . 28 Chapter 4 Modeling multi-phase interactions in a charring ablator using KATS- US .................................. 30 4.1 Motivation . 30 4.2 Formulation . 32 4.3 Model Verification . 43 4.4 Concluding remarks on modeling multi-phase interactions in a charring ablator using KATS-US . 48 Chapter 5 Modeling carbon oxidation of a fiberForm plug . 51 5.1 Formulation . 53 5.2 Results . 63 5.3 Conclusion . 65 Chapter 6 Concluding remarks . 70 6.1 Summary . 70 6.2 Original contributions . 71 6.3 Future work . 72 iv Appendix A Modeling of the remain MISP's for MSL . 74 Appendix B Oxidation effects from the Damk¨ohlerand P´ecletnumber . 76 B.1 Damk¨ohlernumber effects . 76 B.2 P´ecletnumber effects . 77 Bibliography . 78 Vita . 104 v LIST OF FIGURES 1.1 Time progression footage of the atmospheric entry of the Hayabusa space- craft and capsule (identified by the red arrow). 3 1.2 Recent NASA program heat shields. 4 1.3 Material zone degradation for volumetric ablators heat shield . 5 2.1 Energy balance at the ablative material gas-solid interface. 15 2.2 Graphical representation of a control volume of a typical porous decom- posing ablator. 16 2.3 Excerpt from the CMA manual (1) . 20 3.1 Instrumentation of the heat shield of the Mars Science Laboratory entry spacecraft . 22 3.2 Phase change of water as a function of temperature, pressure, and time at the location for the four thermocouples of MISP 2. The time at which pyrolysis reaction at the surface are significant is indicated on each graph by the symbol ................................ 25 3.3 Thermocouple readings for MISP 2 using a modified thermal conductivity model accounting for the presence of water. The new results are compared to the previous results obtained using the estimated PICA conductivity from Mahzari et al. (4), as well as the MISP flight data. 28 4.1 Gas pressure (black) and average molecular weight (blue) inside a closed wall domain as the temperature is increase linearly. As the gas equilibrium changes, the averaged molecular weight follows causing the pressure to increase non-linearly. Once the molecular weight nears a constant value, the pressure change becomes linear. 43 4.2 Comparison of KATS-US (lines) with an equilibrium source term with Mutation++ (symbols). The relaxation time used for this problem ensures chemical equilibrium within the first time-step, τr = τf . 45 4.3 Effect of chemical relaxation time η = δt/τr. Four relaxation rates were se- lected with decreasing orders of magnitude: η = 5 ×10−1 (black), 5×10−2 (blue), 5×10−3 (green), and 5×10−4 (red). As the relaxation rate is de- creased by orders of magnitude, the time necessary for the system to reach equilibrium increases by orders of magnitude. 46 4.4 Effect of solid transfer sticking coefficient ζ. Four sticking coefficient were selected: ζ = 1×10−1, 1×10−2, 3×10−3, and 1×10−3.
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