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Early Stage Melt Ejection in
Laser Percussion Drilling
Presenter:
Harini Patlolla
Co-authors: Profs. Tom A. Eppes & Ivana Milanovic
University of Hartford, USA
Excerpt from the Proceedings of the 2012 COMSOL Conference in Boston
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Project Motivation
• Reduce manufacturing costs of turbomachinery
• Create more consistent hole quality
• Better understand metallurgical side-effects
• Develop methods to produce shaped holes
• 3D multiphysics model?
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Example: Turbine Blade Cooling Holes
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• Each contains interior serpentine channels
• Allows surface film cooling
• Requires thousands of holes
COMSOL Conference Boston, MA October 2012
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Laser Percussion Drilling
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K. H. Leong, “Evolving laser processing applications,” ICALEO Conference Proceedings ICALEO, Jacksonville, FL, 2003.
COMSOL Conference Boston, MA October 2012
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COMSOL Conference Boston, MA October 2011
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Multiphysics Modeling Procedure
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Non-isothermal Flow in Fluids
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where u = velocity vector (m/s) p = pressure (Pa) ρ = density (kg/m3) µ = dynamic viscosity (Pas) F = body force (gravity) (N/m3) Cp = specific heat (J/kgK) T = absolute temperature (K) k = thermal conductivity Q = incident heat source (W/m2)
2( ) [ ( ( ) ( ) ]
3
uu u pI u u u I F
t
( ) 0
ut
( )p pT
C C u T k T Qt
COMSOL Conference Boston, MA October 2012
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Physical Dimensions & Mesh
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Region Width (mm) Height (mm)
Air 3 6
Target 3 3
COMSOL Conference Boston, MA October 2012
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Material Properties (Iron)
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Parameter Value
Thermal conductivity (W/mK) 76.2
Ratio of specific heat 1.4
Initial temperature (K) 1,000
Melting temperature (K) 1,808
Vaporization temperature (K) 3,100
Phase change transition range (K) 50
Latent heat of melt (kJ/kg) 247
Latent heat of vaporization (kJ/kg) 6088
COMSOL Conference Boston, MA October 2012
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Additional Material Properties (Iron)
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Parameter Value
Dynamic Viscosity (Pa-s)
- Solid 1
- Liquid, Gas 0.006
Density (kg/m^3)
- Solid, Liquid 7,870
- Gas p/(Rspec*T)
COMSOL Conference Boston, MA October 2012
Heaviside functions used to transition properties from solid liquid gas.
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Velocity vs. Time
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• Nd:YAG laser
• 800 W output power
• 1,000K ambient
• Normal incidence
• Gaussian beam profile
• Parallel polarization
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Surface Temperature Distribution (3.2 msec)
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Maximum temperature = 3,089K
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Total Velocity (3.2 msec)
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Maximum velocity = 66 m/s
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Particle Flow From Target Interior (3.2 msec)
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50 µm below target’s surface
COMSOL Conference Boston, MA October 2012
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Horizontal Motion (3.2 msec)
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Vertical Motion (3.2 msec)
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Liquid Fraction (3.2 msec)
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Vapor Fraction (3.2 msec)
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Conclusions
• Early stages of melt and evaporation investigated
• Phase transitions created with temperature dependent properties
• Time dependent studies performed for iron as the target
• Surface temperature and velocity fields computed
• Early stage target material flows illustrated
• Target liquid & vapor fractions identified
COMSOL Conference Boston, MA October 2012
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Thanks!
Questions? Comments? Feedback?
COMSOL Conference Boston, MA October 2012