The Treatment of Relative Dispersion Within a Combined Puff-Particle Model (PPM)
The Puff-Particle Model (PPM) combines the advantages of both, puff and particle dispersion models. In short, in this approach the centre of mass of each puff is moved along a ‘particle trajectory’, so trying to mimic the quickly changing turbulent flow field. However, particle models account for dispersion of turbulent eddies of all sizes (1 -particle statistics, absolute dispersion) while puff models use relative dispersion to describe the puff growth. Therefore, on combining these two approaches as described above, the dispersing effect of small eddies (smaller than approximately the puff’s size) is accounted for twice. A method is therefore presented to correctly simulate the relative dispersion of puffs within the framework of the PPM. It is based on removing the effect of the high-frequency part of the spectrum when using a ‘particle trajectory’ as the trajectory of the puff centre. It is shown on the basis of tracer data, that the correct treatment and interpretation of the two contributions to the dispersion process is crucial for reproducing experimental results to a good correspondence.
KeywordsRelative Dispersion Kalman Filter Particle Model Turbulent Velocity Tracer Experiment
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