Thermal Modeling of In-Depth Thermocouple Response in ...Thermal Modeling of In-Depth Thermocouple...
Transcript of Thermal Modeling of In-Depth Thermocouple Response in ...Thermal Modeling of In-Depth Thermocouple...
Thermal Modeling of In-Depth
Thermocouple Response in Ablative
TPS Materials
Thermal & Fluids Analysis Workshop (TFAWS 2008)
San Jose State University, San Jose, CA
August 18, 2008
Jose A. Santos Robin A. Beck Timothy K. Risch
Sierra Lobo, Inc. NASA Ames Research
Center
NASA Dryden Flight
Research Center
2
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
• Acknowledgments
Background
3
• MEDLI is an instrumentation suite installed in the heat shield of
the Mars Science Laboratory (MSL) Entry Vehicle that will
gather data on the atmosphere and on aerothermal, Thermal
Protection System (TPS) and aerodynamic characteristics of the
MSL Entry Vehicle during entry and descent providing
engineering data for future Mars missions.
• MEDLI consists of 7 pressure ports and 7 integrated sensor
plugs (containing four thermocouples and an isotherm sensor)
all installed in the forebody heat shield of the MSL entry vehicle.
Cruis e S tage
Backs he ll
Des cent S tage
Rover
Heats hie ld
Cruis e S tage
Backs he ll
Des cent S tage
Rover
Heats hie ld
MSL (For Reference)
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
4
Figure courtesy K. Edquist (NASA LaRC)
c/o R. Beck (NASA ARC)
1. Apex (reference heat flux)
2. Stagnation point
3. Windward heating
augmentation
4. Leeward shoulder heating
5. Leeward shoulder heating
6. Transition onset cusp
7. Leeward acreage recession
MISP Locations:
• Sensors located so as to
provide enough information to
recreate heat flux distribution on
the centerline
Problem Description and Solution Approach
• How does one model the response of the thermocouples
embedded in the fully decomposing thermal protection system
material?
– Existing material response codes do not account for multi-
dimensional pyrolysis gas flow (even the available multi-
dimensional codes still assume one-dimensional pyrolysis gas flow
through the material)
• Conservative approach is taken:
– Compute surface recession and wall temperature boundary
conditions using a 1D material response program and input into a
2D thermal model of the instrumented sensor plug
5
CFD Trajectory
Output:
ρeUeCH(t)
Pw(t)
Hr(t)
Hw(t)
1D Material Response
Code Output:
ds(t)/dt
Tw(t)
Thermal FEM output:
TTC
TTPS
Focus of this presentation
Surface Boundary Conditions to CMA04 Material
Response Program
• Time-dependent input heating and surface pressure profiles
(trajectory considered early in the design of the MSL heat
shield)
6
0
50
100
150
200
250
0 50 100 150 200
Heat Flux (W/cm
2)
Time (s)
Peak Heating
Stagnation Heating
0
5
10
15
20
25
30
35
0 50 100 150 200Surface Pressure (kPa)
Time (s)
Peak Heating
Stagnation Heating
• Peak heating profile: qmax = 217 W/cm2, Pmax = 23 kPa
• Stagnation point heating profile: qmax = 48 W/cm2, Pmax = 30 kPa
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:
7
Peak Heating Profile
0
500
1000
1500
2000
2500
3000
0.000
0.005
0.010
0.015
0.020
0.025
0 50 100 150 200 250
Surface Temperature (K)
Recession rate (mm/s)
Time (s)
Recession rate
Surface Temperature
Stagnation Point Heating Profile
0
500
1000
1500
2000
2500
3000
0.000
0.005
0.010
0.015
0.020
0.025
0 50 100 150 200 250
Surface Temperature (K)
Recession rate (mm/s)
Time (s)
Recession rate
Surface Temperature
• Predicted total recession in peak heating case is only 1.22 mm;
consequently, no thermocouples burn through
• No recession is predicted for the stagnation point
Geometry for 2D Thermal Model
• Thermocouple is modeled as a two-dimensional
object based on its cross-section
8
“Land length”
Bead weld
MISPTC Depth
U-shape Cross Section
y
z
x
z
“L-shape” design:
L-shape Cross Section
y
z
Horizontal
z
x MISP
Coated TC
wire
TC wire
x
y
∞
TPS
z
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 zero
• Material properties are input as functions of temperature
– Virgin properties of SLA-561V from the High Fidelity Response Model
developed at NASA ARC are used
• Material Stack-up:
9
RTV-560
(0.254 mm thick)
SLA-561V
(22.86 mm thick)
2024 Aluminum
(6.35 mm thick)
TC Cross-section
∑
∑=
i
ii
i
ipii
eqpA
CA
Cρ
ρ ,
,
∑
∑=
i
i
i
ii
eqA
kA
k
∑
∑=
i
i
i
ii
eqA
A ρ
ρ
Thermal Model Details (cont’d)
• Computational tool for 2D model:
COMSOL Multiphysics
– Commercial finite-element
package
• User may use pre-defined
physics modules
(transient conduction)
and/or input differential
equations in coefficient or
general form
– Arbitrary Lagrangian-Eulerian
(ALE) moving boundary is
used to provide recession rate
and surface temperature
boundary conditions as a
function of time
– Multiphysics capability of
COMSOL couples moving
mesh with heat conduction in
a solid material
10
Temperatures are in Kelvin
Screenshot showing surface recession of L-shape TC
configuration at time t = 70 sec of the peak heating profile
Thermal Model Details (cont’d)
• Mesh construction
– Approx. 4000 triangular elements total• ~ 75 elements for the alumina coating
• ~ 140 elements for the thermocouple wire
11
Examination of 2D Assumptions
• Assumption of no internal decomposition examined with 1D
dimensional 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 CFD
12
0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250
Time (s)
Temp (K)
Lines: Fully decomposing analysis with surface energy balance
Symbols: Non-decomposing analysis with Tsurf and sdot defined
Tsurf
0.1"
0.2"
0.3" 0.4"
0.5"
0.9"
Peak heating
point
• Fully decomposing trace
lags behind the non-
decomposing result
• Expect 2D non-
decomposing thermal
model to be conservative:
actual thermocouple
response time should be
faster than what the
computations predict
Model Traceability
• Comparison of COMSOL predicted in-depth temperatures with
CMA04 non-decomposing analysis:
13
0
500
1000
1500
2000
2500
0 50 100 150 200 250
Temp (K)
Time (s)
COMSOL TC1
COMSOL TC2
CMA Non-decomposing, TC1
CMA Decomposing, TC1
CMA Non-decomposing, TC2
CMA Decomposing, TC2TC1 (2.54 mm)
TC2 (5.08 mm)
Peak heating
Peak Heating Profile
0
500
1000
1500
2000
2500
0 50 100 150 200 250
Temp (K)
Time (s)
COMSOL TC1
COMSOL TC2
CMA Non-decomposing, TC1
CMA Decomposing, TC1
CMA Non-decomposing, TC2
CMA Decomposing, TC2TC1 (2.54 mm)
TC2 (5.08 mm)
Stagnation point heating
Stagnation Point Heating Profile
• Analysis Matrix (valid for both peak heating and stagnation point heating profiles):
Test Cases
• Thermocouple error is relative to the temperature the TPS would achieve in the absence of instrumentation and subjected to the same boundary conditions
• Analysis focuses on locations of TC1 and TC2: 2.54 mm and 5.08 mm, respectively, from the top surface of the sensor plug
– Since negligible error (< 3 K) is seen at the TC3 location (11.43 mm depth), analysis of TC4 (17.78 mm depth) was not considered
• Aluminum back plate, RTV-560 bonding agent remained isothermal
14
100/)(% ×−= TPSTCTPS TTTError
0.165 mm 0.305 mm 0.396 mm No TC
U-shape × × × ×
L-shape × ×
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 300Temp (K)
Time (s)
U-shape 0.165 mm TC2
U-shape 0.305 mm TC2
U-shape 0.396 mm TC2
L-shape 0.305 mm coated TC2
U-shape no TC2
Peak heatingPeak heating
TC 1 Depth of 2.54 mm from Surface TC 2 Depth of 5.08 mm from Surface
Results – Peak Heating Profile
• Results of parametric studies run to determine effect of wire
diameter and thermocouple installation method
16
• Only the 0.165 mm diameter wire maintains an error below 5% for
the 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 heating
0
2
4
6
8
10
12
14
0 20 40 60 80 100 120 140
Temperature Error (%
)
Time (sec)
U-shape, 0.165-mm wire dia.
U-shape, 0.305-mm wire dia.
U-shape, 0.396-mm wire dia.
L-shape, 0.305-mm coated
5%error
Peak Heating, TC 2
qmax = 217 W/cm2
0
2
4
6
8
10
12
14
0 20 40 60 80 100 120 140
Temperature Error (%
)
Time (sec)
U-shape, 0.165-mm wire dia.
U-shape, 0.305-mm wire dia.
U-shape, 0.396-mm wire dia.
L-shape, 0.305-mm coated
5% error
Peak Heating, TC 1
Curves truncated after 1370 °C
Type K temperature limit
qmax = 217 W/cm2
Results – Stagnation Point Heating Profile
• Lower overall heating at the stagnation point significantly reduces
error for thermocouple configurations
• Only the 0.165 mm and 0.305-in diameter bare wires remain below
an error of 5%
17
0
2
4
6
8
10
0 20 40 60 80 100 120 140
Temperature Error (%
)
Time (sec)
U-shape, 0.165-mm wire dia.
U-shape, 0.305-mm wire dia.
U-shape, 0.396-mm wire dia.
L-shape, 0.305-mm coated
5% error
Stagnation Point Heating, TC 2
qmax = 48 W/cm2
0
2
4
6
8
10
0 20 40 60 80 100 120 140
Temperature Error (%
)
Time (sec)
U-shape, 0.165-mm wire dia.
U-shape, 0.305-mm wire dia.
U-shape, 0.396-mm wire dia.
L-shape, 0.305-mm coated
5% error
Stagnation Point Heating, TC 1
qmax = 48 W/cm2
18
Conclusions
• 2D finite element model constructed in COMSOL
Multiphysics has been developed to estimate the error
associated with thermocouple lag and allows for rapid
turnaround of trade studies
• Moving boundary achieves excellent agreement with
CMA04 for a non-decomposing analysis
• Peak heating location produces larger errors than the
stagnation point (low heating) profile
• Bare wire (uncoated) thermocouple diameters of 0.165
mm and 0.305 mm consistently achieved the best results
among the configurations considered
• No significant thermal lag is predicted with this model for
in-depth thermocouples located at depths 11.43 mm and
below
19
Future Work
• Determine the effect of one thermocouple on another as
a function of separation distance
• Run the model for other trajectories and TPS materials
• Relax the perfect thermal contact assumption and model
the gap between the thermocouple and TPS material
– Radiation between wire and TPS
– Gas flow
• Develop model to account for internal decomposition
with multi-dimensional pyrolysis gas flow
Thermal Model
(Videos)
20
Acknowledgments
• MSL, Entry, Descent, Landing Instrumentation
(MEDLI) project for funding this work
• Dr. Michael J. Wright (NASA-ARC) for providing the
CFD trajectory data input as boundary conditions into
the CMA04 calculations
21
References
• Oishi, T., E. Martinez, and J. Santos. Development and Application of a TPS Recession
Sensor for Flight. AIAA 2008-1219. January 2008.
• Anonymous, User’s Manual Aerotherm Charring Material Thermal Response and Ablation
Program CMA04. ITT Industries, Advanced Engineering & Sciences Division. 2004. ITT
Document No. 1909-04-001.
• Chen, Y.-K. and F. S. Milos. Ablation and Thermal Response Program for Spacecraft
Heatshield Analysis. AIAA 98-0273. 1997.
• Chen, Y.-K. and F. S. Milos. Two-Dimensional Implicit Thermal Response and Ablation
Program for Charring Materials on Hypersonic Space Vehicles. AIAA 2000-0206. 2000.
• Chen, Y.-K. and Frank S. Milos. Three-Dimensional Ablation and Thermal Response
Simulation System. AIAA 2005-5064. 2000.
• “Physical Properties of Chromel-Alumel Alloys.” Cleveland Electric Laboratories. Email
Communication. 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 for
Recovery Vehicles.” SAE Paper 941368, presented at the 24th International Conference on
Environmental Systems and 5th European Symposium on Space Environmental Control
Systems, Friedrichshafen, Germany, June 20-23, 1994.
22