From Ground Testing Facilities to Ablative Heatshields

198 Pages·2014·8.12 MB·English

Advancing EDL Technologies for Future Space Missions:
From Ground Testing Facilities to Ablative Heatshields
Thesis by
Jason Rabinovitch
In Partial Fulfillment of the Requirements
for the Degree of
Doctor of Philosophy
California Institute of Technology
Pasadena, California
2014
(Defended May 16, 2014)
ii
c 2014
(cid:13)
Jason Rabinovitch
All Rights Reserved
iii
Acknowledgments
Firstandforemost,Iwouldliketothankmyadvisor,GuillaumeBlanquart,forworkingwithmeover
the past several years. In addition, I would like to thank my committee members, Tim Colonius,
Beverley Mckeon, and Joe Shepherd, for taking the time to review my work, and for offering many
insightfulcommentsaboutthisthesis. Ithasbeenaprivilegetobesurroundedbysomanyintelligent
people throughout my entire time at Caltech.
In addition, I would like to thank all members of The FORCE and Joe Shepherd’s research
group; this work would not have been possible without the help and support of all of students in
these groups. In particular, I would like to thank Nick Parziale for the time we spent working
together on the Vertical Expansion Tunnel and organizing the Caltech Space Challenge, for many
years of softball, and for his friendship throughout my time at Caltech.
IhavehadtheprivilegeofbeingagraduatestudentfellowoftheKeckInstituteforSpaceStudies
since comingto Caltech. I wouldlike tothank KISSfor funding me during myfirstyearatCaltech,
andfor allowingme to interactwith somany leadersin the aerospaceindustry overthe pastseveral
years. In particular, I would like to thank Michele Judd for making all of these amazing events
possible, and for acting as a professional mentor to me.
The work on ablative heatshields has benefited greatly from collaborations with Vanessa Marx
and R´emy Mevel. To all of my friends from home, from Yale, and from California, thank you for
supporting me all of these years, and for listening to me talk about my research.
Finally,withouttheendlesssupportofmyparents,MarshaandJedRabinovitch,andmybrother,
Marty Rabinovitch, none of this would have been possible. Thank you.
Funding for this work was provided by the U.S. Air Force Office of Scientific Research (Award
FA9550-12-1-0472)under the supervision of Dr. Chiping Li.
iv
Abstract
MotivatedbyrecentMSLresultswheretheablationrateofthePICAheatshieldwasover-predicted,
andstayingtruetothe objectivesoutlinedintheNASASpaceTechnologyRoadmapsandPriorities
report, this work focuses on advancing EDL technologies for future space missions.
Due to the difficulties in performing flight tests in the hypervelocity regime, a new ground
testing facility called the vertical expansion tunnel is proposed. The adverse effects from secondary
diaphragm rupture in an expansion tunnel may be reduced or eliminated by orienting the tunnel
vertically, matching the test gas pressure and the accelerator gas pressure, and initially separating
the test gas from the accelerator gas by density stratification. If some sacrifice of the reservoir
conditions can be made, the VET can be utilized in hypervelocity ground testing, without the
problems associated with secondary diaphragm rupture.
TheperformanceofdifferentconstraintsfortheRate-ControlledConstrained-Equilibrium(RCCE)
method is investigatedin the context of modeling reacting flows characteristicto groundtesting fa-
cilities, and re-entry conditions. The effectiveness of different constraints are isolated, and new
constraints previously unmentioned in the literature are introduced. Three main benefits from the
RCCE method were determined: 1) the reduction in number of equations that need to be solvedto
model a reacting flow; 2) the reduction in stiffness of the system of equations needed to be solved;
and3)theabilitytotabulatechemicalpropertiesasafunctionofaconstraintonce,priortorunning
a simulation, along with the ability to use the same table for multiple simulations.
Finally,publishedphysicalpropertiesofPICAarecompiled,andthecompositionofthepyrolysis
gases that form at high temperatures internal to a heatshield is investigated. A necessary link
between the composition of the solid resin, and the composition of the pyrolysis gases created is
provided. This link, combined with a detailed investigation into a reacting pyrolysis gas mixture,
allows a much needed consistent, and thorough description of many of the physical phenomena
occurring in a PICA heatshield, and their implications, to be presented.
Throughtheuseofcomputationalfluidmechanicsandcomputationalchemistrymethods,signif-
icant contributions have been made to advancing ground testing facilities, computational methods
for reacting flows, and ablation modeling.
v
Contents
Acknowledgments iii
Abstract iv
1 Introduction 1
1.1 Overview of Successful Mars Landings . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2 MSL—Design Considerations and Flight Data . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Organization and Objectives of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3.1 Ground Testing Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3.2 Reacting Flows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3.3 Ablative Heat Shields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2 Vertical Expansion Tunnel 13
2.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Available Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3 Test Time Calculation for the RST and ET . . . . . . . . . . . . . . . . . . . . . . . 19
2.4 Ideal Test Time Calculation for the VET . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.1 The Compressible Euler Equations with Area Change . . . . . . . . . . . . . 21
2.4.2 Roe Solver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4.3 Treatment of Fluid Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.4 Higher-Order Corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4.5 Entropy Fix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.4.6 Numerical Results: Verification . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.4.7 Numerical Results: VET with Nozzle . . . . . . . . . . . . . . . . . . . . . . 29
2.5 Real Facility Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.5.1 Initial Test Gas/AcceleratorGas Separation . . . . . . . . . . . . . . . . . . . 34
vi
2.5.2 Ideal vs. Experimental Test Conditions . . . . . . . . . . . . . . . . . . . . . 34
2.6 Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3 Rate-Controlled Constrained-Equilibrium 38
3.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2 Previous Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3 Reacting Euler Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3.4 RCCE Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.5 Methodology for Constraint Selection . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.5.1 Timescale Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.5.2 Degree of Disequilibrium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.5.3 Effect of Elemental Conservation . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.6 Air Test Cases—Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.6.1 Case #1: Shocked Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3.6.2 Case #2: Steady Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.7 Air Test Cases—ConstraintSelection . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.7.1 Species Constraints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.7.2 Global Quantities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.7.3 Constraints based on Timescale Analysis . . . . . . . . . . . . . . . . . . . . 56
3.7.4 Constraints Based on DOD Analysis . . . . . . . . . . . . . . . . . . . . . . . 59
3.8 Constraint Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
3.8.1 Comparison Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.8.2 Constraint: Individual Species . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.8.3 Constraint: Major and Radical Species. . . . . . . . . . . . . . . . . . . . . . 68
3.8.4 Constraint: Global Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.8.5 Constraint: Timescale Analysis and DOD . . . . . . . . . . . . . . . . . . . . 75
3.8.6 Analysis of Constraint Performance . . . . . . . . . . . . . . . . . . . . . . . 78
3.9 Integrated RCCE Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3.9.1 Methodology for RCCE Simulations . . . . . . . . . . . . . . . . . . . . . . . 83
3.9.2 Tabulated Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
3.9.3 Integrated Simulation Results - Shock . . . . . . . . . . . . . . . . . . . . . . 85
3.9.4 Integrated Simulation Results - Nozzle . . . . . . . . . . . . . . . . . . . . . . 86
3.9.5 Integrated Simulation Results - Discussion. . . . . . . . . . . . . . . . . . . . 88
vii
3.10 Extension to the Martian Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . 89
3.11 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4 Pyrolysis Gas Composition in PICA Heatshields 99
4.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.2 Ablation Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
4.3 PICA Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
4.3.1 Expected Fiber Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
4.3.2 Expected Resin Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
4.3.2.1 Types and Production . . . . . . . . . . . . . . . . . . . . . . . . . . 105
4.3.2.2 Curing and Thermal Decomposition . . . . . . . . . . . . . . . . . . 107
4.3.2.3 Presence of Impurities . . . . . . . . . . . . . . . . . . . . . . . . . . 108
4.3.3 Expected Char Composition. . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
4.4 Pyrolysis Gas Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.4.1 Equilibrium Pyrolysis Gas Composition . . . . . . . . . . . . . . . . . . . . . 111
4.4.1.1 Gas Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
4.4.1.2 Elemental Composition of Pyrolysis Gases . . . . . . . . . . . . . . 113
4.4.1.3 Equilibrium Results—PAH Species. . . . . . . . . . . . . . . . . . . 114
4.4.1.4 Equilibrium Results—Varying Mixture Composition . . . . . . . . . 115
4.4.1.5 Equilibrium Results—Discussion . . . . . . . . . . . . . . . . . . . . 118
4.4.2 Kinetic Evolution of Pyrolysis Gas Composition . . . . . . . . . . . . . . . . 119
4.5 Pyrolysis Gas Flow Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
4.5.1 Continuum Flow Assumption . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
4.5.2 PAH Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4.5.3 PAH and Fiber Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
4.6 Effect of Carbon Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
4.6.1 Model #1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
4.6.2 Model #2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
4.6.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
4.7 Analysis of Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
4.8 Constrained Equilibrium Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . 139
4.9 Summary and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
viii
5 Conclusions and Future Work 147
5.1 Vertical Expansion Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
5.2 Rate-Controlled Constrained-Equilibrium . . . . . . . . . . . . . . . . . . . . . . . . 148
5.3 Pyrolysis Gas Composition in PICA Heatshields . . . . . . . . . . . . . . . . . . . . 149
Appendices 167
A Constrained Thermodynamic Equilibrium Calculations 168
B RCCE Table Sensitivity 169
C Resin Synthesis 172
C.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
C.2 Curing and Decomposition Characteristics . . . . . . . . . . . . . . . . . . . . . . . . 173
C.3 Synthesis of Novolac Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
C.3.1 Brønsted Acid Catalysts—NovolacResins . . . . . . . . . . . . . . . . . . . . 176
C.3.2 Lewis (Neutral) Acid Catalysts—High Ortho Novolac Resins . . . . . . . . . 176
C.4 Synthesis of Resole Resins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
C.5 Byproducts formed in synthesis of resins . . . . . . . . . . . . . . . . . . . . . . . . . 179
D Pyrolysis Gas Model 182
ix
List of Figures
1.1 Three Generations of Mars Rovers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 MSL Flight Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3 Secondary Diaphragm Impacts in an Expansion Tube . . . . . . . . . . . . . . . . . . 8
1.4 Avcoat and PICA Pyrolysis Gas Compositions . . . . . . . . . . . . . . . . . . . . . . 11
2.1 Expansion Tunnel Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2 Pressure-Velocity Diagram for a Conventional Expansion Tube . . . . . . . . . . . . . 17
2.3 Pressure-Velocity Diagram for a Vertical Expansion Tunnel . . . . . . . . . . . . . . . 17
2.4 Schematic x-t Diagram for a Conventional ET . . . . . . . . . . . . . . . . . . . . . . 20
2.5 Numerical Flux Correction for Fluid Interfaces . . . . . . . . . . . . . . . . . . . . . . 25
2.6 1D Numerical x-t Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.7 Analytic and Numerical Test Time Comparison. . . . . . . . . . . . . . . . . . . . . . 29
2.8 Numerical x-t Diagram for an Expansion Tunnel . . . . . . . . . . . . . . . . . . . . . 30
2.9 x-t Diagram for Accelerator and Nozzle Sections . . . . . . . . . . . . . . . . . . . . . 31
2.10 Test Time Calculations for the VET . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.11 VET Normalized Flow conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.1 Overview of RCCE Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2 Species Evolution for Shocked Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.3 Species Evolution for Expanding Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.4 Reaction Mode Time Scales for Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.5 Reaction Coefficients for Air—Fast Mode . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.6 Degree of Disequilibrium for Air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.7 Shocked Air—Constraining O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2
3.8 Shocked Air—Constraining N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2
3.9 Shocked Air—Constraining NO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
x
3.10 Shocked Air—Constraining O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.11 Expanding Air—Constraining O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2
3.12 Expanding Air—Constraining N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2
3.13 Expanding Air—Constraining O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.14 Expanding Air—Constraining NO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.15 Shocked Air—Constraining Major Species . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.16 Shocked Air—Constraining Radical Species . . . . . . . . . . . . . . . . . . . . . . . . 69
3.17 Expanding Air—Constraining Major Species . . . . . . . . . . . . . . . . . . . . . . . 69
3.18 Expanding Air—Constraining Radical Species . . . . . . . . . . . . . . . . . . . . . . 70
3.19 Shocked Air—Constraining Molecular Weight . . . . . . . . . . . . . . . . . . . . . . . 71
3.20 Shocked Air—Constraining Standard Enthalpy of Formation (by Mass) . . . . . . . . 72
3.21 Expanding Air—Constraining Molecular Weight . . . . . . . . . . . . . . . . . . . . . 74
3.22 Expanding Air—Constraining Standard Enthalpy of Formation (by Mass) . . . . . . . 74
3.23 Shocked Air—Constraining Using Fast Reaction Mode . . . . . . . . . . . . . . . . . . 75
3.24 Shocked Air—Constraint Based on DOD Analysis and Elemental Conservation . . . . 76
3.25 Expanding Air—Constraining Using Fast Reaction Mode . . . . . . . . . . . . . . . . 76
3.26 Expanding Air—Constraint Based on DOD Analysis and Elemental Conservation . . 77
3.27 L2 Error Plot Air—h(T ) and γ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
o
3.28 Weighted L2 Error Plot Air—h(T ) and γ . . . . . . . . . . . . . . . . . . . . . . . . . 80
o
3.29 L2 Error Plot Air—∂φ/∂t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
| |
3.30 Reconstruction of φ—Constraining Enthalpy of Formation. . . . . . . . . . . . . . . . 82
3.31 RCCE Simulation for a Shocked Gas (Mass Fractions) . . . . . . . . . . . . . . . . . . 86
3.32 RCCE Simulation for a Shocked Gas (Constraint) . . . . . . . . . . . . . . . . . . . . 87
3.33 RCCE Simulation for a Diverging Nozzle (Mass Fractions) . . . . . . . . . . . . . . . 87
3.34 RCCE Simulation for a Diverging Nozzle (Constraint) . . . . . . . . . . . . . . . . . . 88
3.35 Species Evolution for Martian Atmosphere Processedby a Normal Shock . . . . . . . 90
3.36 Species Evolution for Martian Atmosphere Undergoing a Steady Expansion . . . . . . 91
3.37 Shocked Mars Atmosphere—Constraining Enthalpy of Formation (by Mass) . . . . . . 92
3.38 Expanding Mars Atmosphere—Constraining Enthalpy of Formation (by Mass) . . . . 92
3.39 L2 Norm Comparisons for Mars Atmosphere . . . . . . . . . . . . . . . . . . . . . . . 93
3.40 Reconstruction of φ (Mars Atmosphere) . . . . . . . . . . . . . . . . . . . . . . . . . . 94
3.41 RCCE Simulation for a Shocked Flow—Mars (Mass Fractions) . . . . . . . . . . . . . 95