Engineering Commons^™

An Adjoint Method To Determine The Effective Material Properties Of An Ablator, Emma Johnstone

Ablation Workshop

The determination of the effective thermal properties of a material from thermocouple data has always been very labour intensive. Similarly determining the Arrhenius parameters for a decomposition model from thermo-gravimetric analysis is also very time-consuming. There is little formalisation of the procedures used to determine the material properties. Despite the fact that some effort has been devoted to this topic in the literature, it is not clear whether comparable effective material properties data would result if several groups used the same experimental data. The FGE Ablation code FABL has been written in an adjoint form and has successfully been used …

Ultrasonic Thermometry For Recession Measurements In Ablative Materials, Joseph A. Lloyd, Donald E. Yuhas

Ablation Workshop

Recent developments in ultrasonic instrumentation & sensors, improved signal processing, and high speed data acquisition have rekindled interest in ultrasonic thermometry and made temperature localization feasible and economically attractive to a wider range of applications. Ultrasound-based temperature measurements offer several advantages: they are non-intrusive, have high temporal response, isolate the sensor from explosive or chemically harsh environments and do not adversely influence thermal transport. Ultrasonic thermometry techniques rely on precise measurements of ultrasonic time-of-flight (ToF) which forms the basis for many applications including measurements of flow, heat flux, temperature, ablation and strain. In this report, we characterize the ultrasonic propagation …

A Statistics-Based Material Property Analysis To Support Ablation Simulation Uq Efforts, Sean R. Copeland, Juan Alonso, Milad Mahzari, Ioana Cozmuta

Ablation Workshop

Accurate characterization of entry capsule heat shield material properties is a critical component in modeling and simulating Thermal Protection System (TPS) response in a prescribed aerothermal environment. The thermal decomposition of the TPS material during the pyrolysis and charring processes is typically poorly characterized and results in large uncertainties in material properties as inputs for ablation models. These material property uncertainties contribute to large design margins on flight systems and cloud re-construction efforts for data collected during flight and ground testing, making revision to existing models for entry systems more challenging. This work focuses on the following areas of interest …

Efficient Uncertainty Quantification & Sensitivity Analysis For Hypersonic Flow And Material Response Simulations Under Inherent And Model-Form Uncertainties, Serhat Hosder

Ablation Workshop

Accurate numerical prediction of coupled hypersonic flow fields and ablative TPS material response is challenging due to the complex nature of the physics. The uncertainties associated with various physical models used in high-enthalpy hypersonic flow and material response simulations can have significant effects on the accuracy of the results including the heat-flux and temperature distributions in various layers of ablating TPS material. These uncertainties can arise from the lack of knowledge in physical modeling (model-form or epistemic uncertainty) or inherent variations in the model inputs (aleatory or probabilistic uncertainty). It is important to include both types of uncertainty in the …

Ablative Thermal Protection System (Tps) Margin Study, Steven Rickman, Lawrence Green, Brian Remark, Stan Bouslog, Jeremy Vander Kam, Mohammad Khalessi

Ablation Workshop

Predicting the reliability of the heat shield for crewed space vehicles has been a topic of continuing interest within NASA for many years. The design of a thermal protection system (TPS) is subject to numerous large sources of uncertainty and reliability assessments of such TPS are rare. The proposed talk discusses both the application of Design Of Experiments (DOE) to developing a new arc jet testing campaign for a given TPS and the reliability assessment conducted for the same TPS for a crewed space capsule (similar to Apollo capsules) to withstand re-entry to earth from space.

The objectives of the …

Study Of Mechanical And Thermal Behavior Of Polymeric Ablator Using Md, Abhishek Kumar, Veera Sundararaghavan

Ablation Workshop

The thermal protection materials used for spacecraft heat shields are subjected to various thermal and mechanical loads during an atmospheric entry which can threaten the structural integrity of the system. This paper describes the development of a molecular dynamics approach to understand the mechanical and thermal behavior of high temperature polymers. One such material PICA has successfully flown on the Stardust spacecraft and is the TPS material chosen for the Mars Science Laboratory (MSL) and SpaceX Dragon spacecraft. Although such polymers have good structural properties at moderate temperature,they became structurally weak at extreme region of temperature and loads. In order …

Aerothermal Characterization Of Silicon Carbide-Based Tps In High Enthalpy Airflow, Francesco Panerai, Olivier Chazot

Ablation Workshop

Inductively-coupled plasma generators provide an ideal environment to reproduce the aerothermal heating experienced by a spacecraft re-entering a planetary atmosphere. The flight boundary layer chemistry is duplicated around a TPS model, ensuring a similarity between the flight and ground stagnation-point heat flux.

Experiments conducted in an induction plasmatron on silicon carbide-based thermal protection materials will be described. Several specimens are tested under a wide range of pressure and temperature conditions and investigated by means of infrared radiometry and optical emission spectroscopy. The plasma to which the materials are exposed is characterized in details by calorimetric and Pitot pressure measurements, and …

Methodology For Ablation Investigations In The Vki Plasmatron Facility: Preliminary Results With A Carbon Fiber Preform, Bernd Helber, Olivier Chazot, Annick Hubin, Thierry Magin

Ablation Workshop

Following the current developments of a new class of low-density, carbon/resin composite ablators, new efforts were initiated at the VKI on ablation research to understand the complex material response under reentry conditions and to develop and validate new material response models. Promising experimental results were obtained by testing the low-density monolytic composite ablator (MonA) in the 1.2MW inductively heated VKI Plasmatron facility. The application of a high speed camera with short exposure times (2μs) enabled in-situ analysis of both (3D) surface recession and spallation and further made it possible to demonstrate the outgassing effects of pyrolizing ablators. A change in …

Thermo-Chemical And Mechanical Coupled Analysis Of Swelling, Charring And Ablative Materials For Re-Entry Applications, Gregory Pinaud

Ablation Workshop

One of the major challenges in the design of atmospheric reentry vehicles is the optimization of the thermal protection system (TPS). During a reentry, the vehicle encounter severs heating and mechanical stress. A robust sizing is therefore essential to insure vehicle integrity and the mission success. In order to maximize the payload mass of the vehicle, lightweight charring ablators are commonly chosen as TPS materials for this one shot mission.

To predict the behaviour of the TPS ablative materials under pyrolysis for reentry applications, Astrium ST initiated the development of a specific module of the finite element software SAMCEF: AMARYLLIS. …

Coupled Computation Of Fluid And Material Response For Non-Charring Ablative Materials In Hypersonic Flow, Jonathan E. Wiebenga, Iain D. Boyd

Ablation Workshop

Hypersonic vehicles are subjected to high heat loads throughout their flight trajectories, and as a result, some form of thermal protection system (TPS) is required to ensure the vehicle’s survival. Accurate prediction of the behavior of these materials in a hypersonic environment is crucial to the efficient design of a hypersonic flight vehicle. It can be very costly and difficult, however, to experimentally replicate the flow conditions found in many hypersonic regimes, and for this reason it is desirable to be able to simulate the behavior of TPS materials under these flight conditions. This study aims to improve the modeling …

Uncertainty Analysis Of Reaction Rates In A Finite Rate Gas-Surface Model, Thomas E. Schwartzentruber

Ablation Workshop

A finite–rate–catalytic wall boundary condition incorporated into hypersonic flow simulations is investigated. Benchmark simulations of hypersonic flow over a cylinder are presented using the finite–rate–catalytic model parameterized with a test air–silica chemical model comprising the gas–surface reaction mechanisms and their associated rates. It is demonstrated that backwards recombination rates should not be arbitrarily set but must be consistent with the gas–phase thermodynamics, otherwise a drift from the equilibrium state may occur. The heat flux predicted by the finite rate model lies between non–catalytic and super–catalytic limits depending on the surface temperature. It is found that even for a constant surface …

Cfd Ablation Predictions With Coupled Gsi Modeling For Charring And Non-Charring Materials, Daniele Bianchi, Alessandro Turchi, F. Nasuti, M. Onofri

Ablation Workshop

To this day, a major objective of TPS design is to reduce empiricism, and to increase fundamental modeling capability through increased understanding. One of the most challenging aspect is the proper coupling between the material response and the external flow field. With this regard, the goal of this research activity is the improvement of the numerical modeling capabilities through the development of advanced CFD tools integrated with Gas-Surface Interaction (GSI) modeling.

Numerical prediction of ablation is ambitious and cpu-time demanding due to the complex multiphase physical and chemical processes that occur. With improvements in computational algorithms and advances in computer …

Radiative Transfer Equation Solver Module For Coupled Simulation Of Hypersonic Flows, Ranjan S. Mehta, Paul J. Dionne, Samuel F. Owens

Ablation Workshop

Accurate numerical modeling of the aerothermal environment around an ablation-cooled hypersonic re-entry vehicle requires high-fidelity models for processes such as non-equilibrium surface themochemistry, non-equilibrium pyrolysis chemistry, multi-scale radiation, spallation and charring. It is expected that, these models when utilized in a coupled manner will be able to accurately capture the possible nonlinear interactions between various phenomena in a computationally efficient manner. Development of a coupled radiative solver is currently being carried out as part of a joint effort between CFDRC, University of Michigan and University of Kentucky to develop a fully coupled method of simulating atmospheric entry flows and response …

Modeling Of Heat Transfer Attenuation By Ablative Gases During The Stardust Re-Entry, Alexandre Martin, Iain D. Boyd

Ablation Workshop

The great majority of modern space vehicles designed for planetary exploration use ablative materials to protect the payload against the high heating environment experienced during re-entry. In order to properly model and predict the aerothermal environment of the vehicle, it is imperative to account for the gases produced by ablation processes. In the case of charring ablators, where an inner resin is pyrolyzed at a relatively low temperature, the composition of the gas expelled into the boundary layer is complex and may lead to thermal chemical reactions that cannot be captured with simple flow chemistry models. In order to obtain …

Ablation Modeling Of A Solid Rocket Nozzle, Mark E. Ewing, Galen H. Richards, Micheal P. Iverson, Daron A. Isaac

Ablation Workshop

No abstract provided.

Definition Of Ablation Test-Case Series #3, Tom Van Eekelen, Jean R. Lachaud, Alexandre Martin, Ioana Cozmuta

Ablation Workshop

The test-case series #3 will be a further extension of the tests defined within the framework of the NASA ablation modelling workshops. In order to reduce the amount of work, all tests within test-case series #3, will use the TACOT material defined by Lachaud et al. The main goal of this new series, is to test the 3D modelling capabilities of the participating codes. The first 1D results were presented at the 4th Ablation workshop, and together with the results of the second test-case series, will be discussed and analyzed more thoroughly at the 5th Ablation Workshop, Feb. 28- March …

Ablation Test Case Series #2. Mopar: Results For The Inter-Code Calibration, Jonathan E. Wiebenga, Iain D. Boyd, Alexandre Martin

Ablation Workshop

No abstract provided.

Ablation Test Case Series #2. Itrac Results, Mark E. Ewing

Ablation Workshop

No abstract provided.

Ablation Test Case Series #2. Amaryllis Results, Tom Van Eekelen, Jean-Marc Bouilly

Ablation Workshop

No abstract provided.

Ablation Test Case Series #2. Test Case Baseline Results, Tim Risch, Chris Kostyk

Ablation Workshop

No abstract provided.

Ablation Test Case Series #2. Are The Test Problems Well Posed With Ch = Cm = 0?, Ben F. Blackwell

Ablation Workshop

No abstract provided.

Ablation Test Case Series #2. Be13 Results, Jean-Marc Bouilly

Ablation Workshop

No abstract provided.

Prediction Of Tacot Decomposition Using The Chaleur Code, Ben F. Blackwell, Micah Howard

Ablation Workshop

This talk will briefly discuss the ablation thermochemistry data used for the TACOT code comparison test cases. Three areas of interest will be highlighted: codes and numerical methods for solving the thermochemical equilibrium problem, differences in ablation thermochemistry data (Bc and enthalpy) when using the CEA and JANAF databases, and the effect of the choice of pyrolysis gas species will be discussed.

A Perspective On The Design And Development Of The Spacex Dragon Spacecraft Heatshield, Daniel J. Rasky

Ablation Workshop

In December, 2010, Space Exploration Technologies (SpaceX) successfully orbited, re-entered and recovered their Dragon spacecraft, on an almost “picture perfect” first full mission. Earlier in 2009, SpaceX, announced the passing of a significant technical milestone with the successful arc jet testing of a their new high performance heat shield material, called PICA-X, which provided the primary (forebody) thermal protection for Dragon.

In 2008 and 2009, Dr. Rasky worked closely with SpaceX on the Dragon heatshield design and also developing the ability to manufacture PICA-X. The “X” stands for the SpaceX-developed variants that have several improved properties and greater ease of …

The Mysteries Of Real Materials, Bernard Laub

Ablation Workshop

The presentation will consist in showing arc jet data mysterious to the modelers. It will show a short movie (10-20 sec) of an arc jet test where a material exhibited a failure mode that nobody understands followed by thermocouple data from arc jet tests on another material of interest in which the T/Cs exhibit repeatable, consistent, fascinating yet frustrating response characteristics that have the modelers stumped. This all happens between RT and 200 F. Doesnt sound important? Unless we figure out what it is and can model it, we can’t size the TPS with any confidence.

Characterization Of Material Response During Arc-Jet Testing With Optical Methods–Status And Perspectives, Michael Winter

Ablation Workshop

The characterization of ablation and recession of heat shield materials during arc jet testing is an important step towards understanding the governing processes during these tests and therefore for a successful extrapolation of ground test data to flight. The behavior of ablative heat shield materials in a ground-based arc jet facility is usually monitored through measurement of temperature distributions (across the surface and in-depth), and through measurement of the final surface recession [1, 2]. These measurements are then used to calibrate/validate materials thermal response codes, which have mathematical models with reasonably good fidelity to the physics and chemistry of ablation, …

Sprite: A Tps Test Bed For Ground And Flight, P. Agrawal, A. Cassell, N. Mangini, K. Peterson, Dinesh K. Prabhu, K. Skokova, G. Swanson, D. M. Empey, S. Gorbunov, A. Howard, J. Arnold, E. Venkatapathy

Ablation Workshop

Engineers in the Entry Systems and Technology Division at NASA Ames Research Center developed a fully instrumented, small atmospheric entry probe called SPRITE (Small Probe Reentry Investigation for TPS Engineering). SPRITE, conceived as a flight test bed for thermal protection materials, was tested at full scale in an arc-jet facility so that the aerothermal environments the probe experiences over portions of its flight trajectory and in the arc-jet are similar. This ground-to-flight traceability enhances the ability of mission designers to evaluate margins needed in the design of thermal protection systems (TPS) of larger scale atmospheric entry vehicles.

Development And Validation Of Sacram: A Swiss Approach To The Computational Response Of An Ablative Material, Ojas Joshi, Georges Duffa, Pénélope Leyland

Ablation Workshop

Future space exploration missions foresee high-speed entries into planetary atmospheres. These latter imply extreme thermal conditions to which the space vehicle is exposed to, and require an appropriate thermal protection system (TPS). The interest of the scientific community in modelling and testing of materials that compose the TPS has hence greatly increased over the past few years. Since a complete set of material properties is not available in open literature, it is difficult to numerically rebuild experiments. The inter-code comparison exercise proposed by the AF/SNL/NASA Ablation Workshop aims to give a baseline platform for ablation code calibration, with a complete …

Advanced Thermal Protection Systems (Tps) And Transition Analysis: Unique Experimental Capabilities And Current Research Efforts At The University Of Texas At Arlington, Matthew Crisanti, Cody Ground, Stefano Gulli, Jared Poempipatana, Luca Maddalena

Ablation Workshop

A unique experimental capability in the academic panorama is the 1.6 MW-classic arc-jet facility located at the Aerodynamics Research Center of the University of Texas at Arlington. The arc-heated wind tunnel has recently been refurbished and repurposed (extended testing time of the order of minutes and testing gas-composition control) for the study and characterization of the aerothermal response of TPS candidate materials for sustained hypersonic flight.

Computational Chemistry Modelling Of The Oxidation Of Highly Oriented Pyrolitic Graphite (Hopg), Savio Poovathingal, Thomas E. Schwartzentruber

Ablation Workshop

Under high heat flux, carbon based Thermal Protection Systems (TPS) are observed to rapidly ablate and an accurate characterization is essential to their design. Dissociated oxygen atoms (from the gas phase) striking the surface of TPS could lead to several possibilites. The O atom could adsorb on the surface, recombine with another O atom to form O2 and oxidize the surface to produce CO or CO2 resulting in recession of the surface (ablation). The goal is to predict finite rate models for these reactions which could be incorporated into CFD and DSMC solvers. Our efforts are to predict the rates …