ASC FLASH Collaboration: a Los Alamos Perspective

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ASC FLASH Collaboration a Los Alamos Perspective

• M. Marr-Lyon, C. Tomkins, K. Prestridge
• S. Kumar, C. Goodenough, G. Orlicz, R. Benjamin

Los Alamos team members
Additional collaborators
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The setup offers excellent optical access for
diagnostics
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The experiments are carefully controlled with
relatively simple initial conditions
Test section
Initial condition (idealized)
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Principles of particle image velocimetry (PIV)
to
Image 0
Correlate extracted regions
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Principles of PIV analysis example.
to
t1
Image 0
Image 1
Peak
In 3D
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Sample PIV images

• RM-unstable gas cylinders (taken in DX-3 gas
  shock tube).
• Analysis two-frame cross-correlation
  (Christensen et al., 2000).
• Flow left to right, measurement at late time (6th
  dynamic pulse.)

t1
to
Shock
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Sample PIV velocity vector field

• Convection velocity of structure is subtractedso
  moving in reference frame of vortex
• Approximately 3600 vectors.
• 187 micron vector spacing.

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Vertical plane PIV and velocity contours
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Our interaction with the U. of Chicago ASC center
has been iterative

• We provided them with vertical-plane IC
  information obtained from the PIV inlet
  velocity.
• We also obtained well-resolved dynamic
  measurements in the horizontal plane at late
  time circulation.
• Our collaborative efforts revealed that diffusion
  was playing a key role in the IC evolution
  (simulation, experiment, theory).

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More advanced scalar concentration diagnostic
planar laser-induced fluorescence (PLIF)

• PRINCIPLES
• Mix gas of interest (SF6) with acetone vapor.
• Excite acetone in the uv (266 nm) with laser
  light sheet. Acetone fluoresces in the blue
  (450 nm).
• Instantaneous emission occurs over short time
  scales, 10 ns.
• Estimate local concentration, C(x,y), of SF6 by
  measuring intensity of emitted light.

• ADVANTAGES
• Acetone molecularly mixes with SF6 to faithfully
  trace it.
• Scattered light is uv, so doesnt interfere with
  signal (unlike RS).

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Our diagnostics now extract
high-resolution, quantitative information in a
plane
CONCENTRATION PLIF
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Later, secondary instabilities rapidly
transition the flow to a mixed state (in the
cores)
t 650?s 50, 300
t 880?s 30, 200
t 740?s 50, 200
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Results of the collaboration between LANL and the
ASC FLASH Center

• Experimental and computational efforts have lead
  to an improved understanding of our initial
  conditions.
• The significant three-dimensional effects
  uncovered by the FLASH simulations explain
  important aspects of the data.
• FUTURE
• We are currently modifying our shock tube test
  section to allow vertical plane measurements of
  concentration in addition to velocity.
• Our computational colleagues at LANL are moving
  toward 3-dimensional simulations in this or other
  geometries.