The significance of coherent flow structures for the turbulent mixing ...

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2.4 Particle image analysis
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FIGURE 2.13: Numerical comparison between two-dimensional (solid lines) and three-point Gaussian
peak-fit (graphs with symbols (left column) and dotted lines) with iterative
Ž
Levenberg-Marquardt
pixel) as
method for two fixed particle image displacements (*)Š+7‹ (top: pixel, (*)Š+Œ-0/
bottom:
a function of 6 the -shift. The graph represents the probability density functions for a set of simulated
displacement fields (each 2000 by 16000 pixel in size) analysed with a 2nd order accurate multi-pass
interrogation technique 3 with 3 pixel interrogation window and 50% overlap.
Figure 2.14 shows the distribution obtained by analysing experimental data. The displacement
was achieved by transforming one image as will be outlined in the following chapter. It can
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TABLE 2.1:
between
Comparison
two-dimensional
(bottom row) and threepoint
Gaussian peak-fit for
two particle image displacements
in ) -direction
(centre column (*) +
pixel, right column (*)K+
‹ Ž
-0/ pixel) as a function of
6 the -shift.
33