Microwave ablation compared with radiofrequency ablation ...
Optimization of an Axial Nose-Tip Cavity for Delaying Ablation Onset in Hypersonic Flow
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Transcript of Optimization of an Axial Nose-Tip Cavity for Delaying Ablation Onset in Hypersonic Flow
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Optimization of an Axial Nose-Tip Cavity for Delaying Ablation Onset in Hypersonic Flow
Sidra I. Silton and David B. Goldstein
Center for Aeromechanics Research
The University of Texas at Austin
January 6, 2003
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Motivation• Need for Decreased Heating
– Hypersonic vehicles
– High stagnation point heating
– Ablation causes perturbations in flight path
• Previous Work– Passive method to reduce heating
• Yuceil – experimental
• Engblom – numerical
• Forward-Facing Cavities– Shock oscillations
– Decrease in surface heating
– Cooling Mechanism
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Cooling Mechanism
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Objectives
• Develop understanding of unsteady flow physics– Effect of different cavity geometries
• Surface heating
• Ablation onset
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Experimental Methodology• Wind Tunnel Conditions
– T64K
– Tstag = 370K
– P4693.8Pa
• Model Development– Ice
• fiberglass reinforced
• frozen in LN2
– Mold and spindle
– Shield
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Wind Tunnel Mounted Model
During Tunnel Start After Tunnel Start
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Numerical Methodology• Commercial Codes
– INCA– COYOTE
• Procedure
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Numerical Procedure
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Numerical Methodology• Commercial Codes
– INCA– COYOTE
• Procedure• Assumptions
– Flowfield• Emulate experimental conditions• 2D axisymmetric• Laminar• Isothermal wall temperature of 100K
– Solid Body• 2D axisymmetric• Initial uniform temperature of 100K or 163K (benchmark study)• Ignored sublimation effects• Variable material properties of ice
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Parameter Study
• Extensive Experiments– Simulations for geometry showing
delayed ablation onset
• Nose-Tip Geometry– Dn=2.54 cm
– Cavity Dimensions Investigated• Length, L
• Lip radius, r
• Diameter, D
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L/D Parameter Study
• Experiments– r = 0.795 mm, D = 1.113 cm
– r = 1.191 mm, D = 1.031 cm
– L/D varied from 2.0 to 5.0
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L/D Experimental Results
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L/D Parameter Study
• Experiments– r = 0.795 mm, D = 1.113 cm
– r = 1.191 mm, D = 1.031 cm
– L/D varied from 2.0 to 5.0
• Numerical Simulations– r = 1.191 mm, D = 1.031 cm, L/D = 2.0 (geometry 8)
– r = 1.191 mm, D = 1.031 cm, L/D = 4.0 (geometry 12)
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L/D Numerical Results• Mean bow shock speed decreases with increasing L/D
– Oscillation frequency decreases with increased cavity depth– rms approximately constant
• Mean surface heating increases with L/D– Ablation onset occurs earlier for L/D=4.0
• Shallower cavity may be transitioning in experiments
tonset=1.46 sec
tonset=1.79 sec
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• Experiments– D = 1.27 cm, L/D=3.5, 4.0, 4.5
– r varied from 1.191 mm to 3.175 mm
Lip Radius Parameter Study
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Lip Radius Experimental Results
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• Experiments– D = 1.27 cm, L/D=3.5, 4.0, 4.5
– r varied from 1.191 mm to 3.175 mm
• Numerical Simulations– r = 1.191 mm, D = 1.27 cm, L/D = 4.0 (geometry 24)
– r = 3.175 mm, D = 1.27 cm, L/D = 4.0 (geometry 29)
Lip Radius Parameter Study
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• Pressure waves coalesce into shock– Inside cavity for r = 1.191 mm
• Waves propagate through heat flux
– At cavity lip for r = 3.175 mm
• Mean bow shock speed decreased with increasing lip radius– Oscillation frequency approximately constant
– mean increased with lip radius– rms decreased with increased lip radius
Animation
Animation
mean*
4L
*0 LLwheref RT
osc
Lip Radius Numerical Results
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Lip Radius Mean Heat Flux
tonset=1.5 sec
tonset=3.6 sec
Geometry 24 Geometry 29
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Diameter Parameter Study
• Experiments– D = 0.762 cm, L/D = 4.0
• r = 1.905 mm, 3.175 mm, 4.445 mm
– D = 1.27 cm , L/D = 4.0• r = 1.984 mm, 3.175 mm
– D = 1.778 cm, L/D = 4.0• r = 1.905 mm
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Diameter Experimental Results
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Diameter Parameter Study
• Experiments– D = 0.762 cm, L/D = 4.0
• r = 1.905 mm, 3.175 mm, 4.445 mm
– D = 1.27 cm , L/D = 4.0• r = 1.984 mm, 3.175 mm
– D = 1.778 cm, L/D = 4.0• r = 1.905 mm
• Numerical Simulations– r/(Dn-D) = 0.25, L/D = 4.0
• D = 0.762 cm, 1.27 cm, 1.778 cm (geometries 38, 29, 43)
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Diameter Numerical Results
• Mean bow shock speed decreases with increasing diameter– Oscillation frequency decreased with increasing depth
(L/D=constant)– mean and rms increased with increasing diameter
• Large Diameter Cavity– Pressure waves coalesce into shock inside cavity– Waves propagate through heat flux
• Small Diameter Cavity– Very little bow shock movement– Cavity remains cold (T=250K)
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Diameter Mean Stagnation Temperature
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Diameter Mean Heat Flux
Geometry 43 Geometry 29 Geometry 38
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Diameter Ablation Onset Times
0
1
2
3
4
5
6
7
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
D/Dn
Ab
lati
on
On
set
Tim
e (
sec)
Numerical, Tinit=100K
Numerical, Tinit=163KExperimental
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
D/Dn
CD
Aerodynamic Drag
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Conclusions
• Parameter Study– Experimental parameter study– Computational flow visualization
• Best experimental configurations– Confirms most experimental findings– Flow may indeed be transitioning for sharper cavities
– Optimal nose-tip configuration• Delayed ablation onset
– constant nose diameter means increasing drag– constant drag means decreasing nose diameter
• Geometry– L/D=4.0, r/(Dn-D)=0.25, D/Dn = 0.5