Thermal Modeling Of In-Depth Thermocouple Response In Ablative . - NASA

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Thermal Modeling of In-DepthThermocouple Response in AblativeTPS MaterialsJose A. SantosRobin A. BeckTimothy K. RischSierra Lobo, Inc.NASA Ames ResearchCenterNASA Dryden FlightResearch CenterThermal & Fluids Analysis Workshop (TFAWS 2008)San Jose State University, San Jose, CAAugust 18, 2008

Outline Background and Scope– MSL, Entry, Descent, Landing Instrumentation (MEDLI)– MEDLI Instrumented Sensor Plug (MISP) Two dimensional thermal model– Boundary Conditions– Geometry– Case Studies Conclusions Future Work Acknowledgments2

Background MEDLI is an instrumentation suite installed in the heat shield ofthe Mars Science Laboratory (MSL) Entry Vehicle that willgather data on the atmosphere and on aerothermal, ThermalProtection System (TPS) and aerodynamic characteristics of theMSL Entry Vehicle during entry and descent providingengineering data for future Mars missions. MEDLI consists of 7 pressure ports and 7 integrated sensorplugs (containing four thermocouples and an isotherm sensor)all installed in the forebody heat shield of the MSL entry vehicle.Cruis e S tag eBac ks he llDe s c e nt S tag eRo v e rHe ats hie ldMSL (For Reference)3

MEDLI Instrumented Sensor Plug (MISP) Sensor plug contains four in-depth Type K TCs 2.54 mm,5.08 mm, 11.43 mm, and 17.78 mm from the surface One isotherm-following sensor to measure char depth Sensors located so as toprovide enough information torecreate heat flux distribution onthe centerlineMISP Locations:1. Apex (reference heat flux)2. Stagnation point3. Windward heatingaugmentation4. Leeward shoulder heating5. Leeward shoulder heating6. Transition onset cusp7. Leeward acreage recessionFigure courtesy K. Edquist (NASA LaRC)c/o R. Beck (NASA ARC)4

Problem Description and Solution Approach How does one model the response of the thermocouplesembedded in the fully decomposing thermal protection systemmaterial?– Existing material response codes do not account for multidimensional pyrolysis gas flow (even the available multidimensional codes still assume one-dimensional pyrolysis gas flowthrough the material) Conservative approach is taken:– Compute surface recession and wall temperature boundaryconditions using a 1D material response program and input into a2D thermal model of the instrumented sensor plugCFD TrajectoryOutput:ρeUeCH(t)Pw(t)Hr(t)1D Material ResponseCode Output:Thermal FEM output:ds(t)/dtTw(t)TTPSTTCHw(t)Focus of this presentation5

Surface Boundary Conditions to CMA04 MaterialResponse Program Time-dependent input heating and surface pressure profiles(trajectory considered early in the design of the MSL heatshield)25035Peak HeatingPeak Heating30Surface Pressure (kPa)Heat Flux (W/cm2)200Stagnation Heating15010050Stagnation Heating25201510500050100Time (s)150200050100Time (s)150200 Peak heating profile: qmax 217 W/cm2, Pmax 23 kPa Stagnation point heating profile: qmax 48 W/cm2, Pmax 30 kPa6

2D Heat Conduction Model Boundary Conditions CMA04 material input file– SLA-561V High Fidelity Response Model (HFRM), peer reviewed at NASA ARC,and Mars “B prime tables” (dimensionless mass surface flux) are used Computed wall temperature and recession rate time histories:0.02530000.0253000Recession me (s)Peak Heating ace Temperature (K)2000Surface TemperatureRecession rate (mm/s)2500Surface Temperature0.020Surface Temperature (K)Recession rate (mm/s)Recession rate5000.0000050100150200250Time (s)Stagnation Point Heating Profile Predicted total recession in peak heating case is only 1.22 mm;consequently, no thermocouples burn through No recession is predicted for the stagnation point7

Geometry for 2D Thermal Model Thermocouple is modeled as a two-dimensionalobject based on its cross-sectionMISPTC DepthxU-shape Cross SectionBead weldyxyTPSz “Land length”zMISPxTC wireL-shape Cross Sectionzy“L-shape” design:Coated TCwirezzHorizontal8

Construction of Thermal Model 2-D Boundary conditions for side and back walls– Insulated side walls are assumed– Radiation from back wall to an ambient temperature of 203 K (-70 C)Initial conditions– All materials are set to 203 K at time zeroMaterial properties are input as functions of temperature– Virgin properties of SLA-561V from the High Fidelity Response Modeldeveloped at NASA ARC are usedMaterial Stack-up:TC Cross-section Aρ Aiρ eqSLA-561V(22.86 mm thick)RTV-560(0.254 mm thick)2024 Aluminum(6.35 mm thick)iiii Ai k ik eq i Ai Ai ρ i C p,iC p ,eq i Ai ρ iii9

Thermal Model Details (cont’d) Computational tool for 2D model:COMSOL Multiphysics– Commercial finite-elementpackage User may use pre-definedphysics modules(transient conduction)and/or input differentialequations in coefficient orgeneral form– Arbitrary Lagrangian-Eulerian(ALE) moving boundary isused to provide recession rateand surface temperatureboundary conditions as afunction of time– Multiphysics capability ofCOMSOL couples movingmesh with heat conduction ina solid materialScreenshot showing surface recession of L-shape TCconfiguration at time t 70 sec of the peak heating profileTemperatures are in Kelvin10

Thermal Model Details (cont’d) Mesh construction– Approx. 4000 triangular elements total 75 elements for the alumina coating 140 elements for the thermocouple wire11

Examination of 2D Assumptions Assumption of no internal decomposition examined with 1Ddimensional CMA04 analysis CMA04 code is run for two cases with different boundary conditions: No decomposition – time-dependent surface temperature and recession rate Fully decomposing – ρeUeCH(t), Pw(t), Hr(t), Hw(t) taken from CFD3000Peak heatingpointLines: Fully decomposing analysis with surface energy balanceSymbols: Non-decomposing analysis with Tsurf and sdot defined2500Tsurf2000Temp (K) Fully decomposing tracelags behind the nondecomposing result Expect 2D nondecomposing thermalmodel to be conservative:actual thermocoupleresponse time should befaster than what thecomputations 50200250Time (s)12

Model Traceability Comparison of COMSOL predicted in-depth temperatures withCMA04 non-decomposing analysis:25002500Peak heatingStagnation point heatingCOMSOL TC1COMSOL TC1COMSOL TC2COMSOL TC2CMA Non-decomposing, TC12000CMA Decomposing, TC1CMA Non-decomposing, TC2TC1 (2.54 mm)CMA Decomposing, TC21500Temp (K)Temp (K)CMA Decomposing, TC11000500CMA Non-decomposing, TC12000TC2 (5.08 mm)CMA Non-decomposing, TC2TC1 (2.54 mm)CMA Decomposing, TC215001000500TC2 (5.08 mm)0050100150Time (s)Peak Heating Profile2002500050100150200250Time (s)Stagnation Point Heating Profile13

Test Cases Analysis Matrix (valid for both peak heating and stagnation pointheating profiles):0.165 mm 0.305 mm 0.396 mmU-shapeL-shape No TC Thermocouple error is relative to the temperature the TPS wouldachieve in the absence of instrumentation and subjected to thesame boundary conditions% Error (TTPS TTC ) / TTPS 100 Analysis focuses on locations of TC1 and TC2: 2.54 mm and 5.08mm, respectively, from the top surface of the sensor plug– Since negligible error ( 3 K) is seen at the TC3 location (11.43mm depth), analysis of TC4 (17.78 mm depth) was notconsidered Aluminum back plate, RTV-560 bonding agent remained isothermal14

Thermal Model Simulation Temperature-time histories for peak heating profile:18001800Peak heatingPeak heatingU-shape 0.165 mm TC216001600U-shape 0.305 mm TC214001400U-shape 0.165 mm TC1U-shape 0.396 mm TC21200U-shape 0.396 mm TC1L-shape 0.305 mm coated TC11000Temp (K)Temp (K)U-shape 0.305 mm TC1U-shape no TC180080060040040020020000204060Time (s)TC 1 Depth of 2.54 mm from Surface80U-shape no TC210006000L-shape 0.305 mm coated TC21200050100150200250300Time (s)TC 2 Depth of 5.08 mm from Surface15

Results – Peak Heating Profile Results of parametric studies run to determine effect of wirediameter and thermocouple installation method1414Peak Heating, TC 1Peak Heating, TC 212U-shape, 0.305-mm wire dia.qmax 217 W/cm210L-shape, 0.305-mm coated85% error64Curves truncated after 1370 CType K temperature limit20U-shape, 0.165-mm wire dia.U-shape, 0.305-mm wire dia.qmax 217 W/cm2U-shape, 0.396-mm wire dia.Temperature Error (%)Temperature Error (%)12U-shape, 0.165-mm wire dia.U-shape, 0.396-mm wire dia.10L-shape, 0.305-mm coated85% error6420020406080Time (sec)100120140020406080100120140Time (sec) Only the 0.165 mm diameter wire maintains an error below 5% forthe entire duration of the trajectory In the case of the thermocouple located 5.08 mm from the surface,the error peaks at the time of peak heating16

Results – Stagnation Point Heating Profile1010Stagnation Point Heating, TC 1qmax 48W/cm2U-shape, 0.305-mm wire dia.8q max 48 W/cm645% error2U-shape, 0.305-mm wire dia.8U-shape, 0.396-mm wire dia.L-shape, 0.305-mm coatedU-shape, 0.165-mm wire dia.2Temperature Error (%)Temperature Error (%)Stagnation Point Heating, TC 2U-shape, 0.165-mm wire dia.U-shape, 0.396-mm wire dia.L-shape, 0.305-mm coated645% error200020406080Time (sec)100120140020406080100120140Time (sec) Lower overall heating at the stagnation point significantly reduceserror for thermocouple configurations Only the 0.165 mm and 0.305-in diameter bare wires remain belowan error of 5%17

Conclusions 2D finite element model constructed in COMSOLMultiphysics has been developed to estimate the errorassociated with thermocouple lag and allows for rapidturnaround of trade studies Moving boundary achieves excellent agreement withCMA04 for a non-decomposing analysis Peak heating location produces larger errors than thestagnation point (low heating) profile Bare wire (uncoated) thermocouple diameters of 0.165mm and 0.305 mm consistently achieved the best resultsamong the configurations considered No significant thermal lag is predicted with this model forin-depth thermocouples located at depths 11.43 mm andbelow18

Future Work Determine the effect of one thermocouple on another asa function of separation distance Run the model for other trajectories and TPS materials Relax the perfect thermal contact assumption and modelthe gap between the thermocouple and TPS material– Radiation between wire and TPS– Gas flow Develop model to account for internal decompositionwith multi-dimensional pyrolysis gas flow19

Thermal Model(Videos)20

Acknowledgments MSL, Entry, Descent, Landing Instrumentation(MEDLI) project for funding this work Dr. Michael J. Wright (NASA-ARC) for providing theCFD trajectory data input as boundary conditions intothe CMA04 calculations21

References Oishi, T., E. Martinez, and J. Santos. Development and Application of a TPS RecessionSensor for Flight. AIAA 2008-1219. January 2008.Anonymous, User’s Manual Aerotherm Charring Material Thermal Response and AblationProgram CMA04. ITT Industries, Advanced Engineering & Sciences Division. 2004. ITTDocument No. 1909-04-001.Chen, Y.-K. and F. S. Milos. Ablation and Thermal Response Program for SpacecraftHeatshield Analysis. AIAA 98-0273. 1997.Chen, Y.-K. and F. S. Milos. Two-Dimensional Implicit Thermal Response and AblationProgram for Charring Materials on Hypersonic Space Vehicles. AIAA 2000-0206. 2000.Chen, Y.-K. and Frank S. Milos. Three-Dimensional Ablation and Thermal ResponseSimulation System. AIAA 2005-5064. 2000.“Physical Properties of Chromel-Alumel Alloys.” Cleveland Electric Laboratories. EmailCommunication. January 2007.Anonymous, COMSOL Multiphysics User’s Guide. Version 3.2. September 2005.Standard Practice for Internal Temperature Measurements in Low-Conductivity Materials.ASTM E377-96. Reapproved 2002.Beck, Robin and B. Laub. “Characterization and Modeling of Low Density TPS Materials forRecovery Vehicles.” SAE Paper 941368, presented at the 24th International Conference onEnvironmental Systems and 5th European Symposium on Space Environmental ControlSystems, Friedrichshafen, Germany, June 20-23, 1994.22

Thermal Model Simulation 15 Temperature-time histories for peak heating profile: 0 200 400 600 800 1000 1200 1400 1600 1800 0 20 40 60 80 Temp (K) Time (s) U-shape 0.165 mm TC1 U-shape 0.305 mm TC1 U-shape 0.396 mm TC1 L-shape 0.305 mm coated TC1 U-shape no TC1 Peak heating 0 200 400 600 800 1000 1200 1400 1600 1800 0 50 100 150 200 250 300 .

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