The Accuracy of Remapping Irregularly Spaced Velocity Data onto a Regular Grid and the Computation of Vorticity
MICHIGAN STATE UNIV EAST LANSING DEPT OF MECHANICAL ENGINEERING
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The velocity data obtained from Molecular Tagging Velocimetry MTV are typically located on an irregularly spaced measurement grid. In this method of velocimetry, the flowing medium is premixed with a molecular complex that can be turned into a long life-time tracer upon excitation by photons. The velocity vector is determined from the displacement of small regions tagged by a pulsed laser which are imaged at two successive times within the lifetime of the tracer. This technique may be viewed as the molecular counterpart of PIV. To take advantage of standard data processing techniques, the MTV data need to be remapped onto a regular grid with a uniform spacing. In this work we examine the accuracy and noise issues related to the use of various low order polynomial least square fits for remapping and the subsequent computation of vorticity from these data The information obtained has relevance to PIV data processing as well. As noted by Spedding and Rignot 1993, the best estimate of the location of the velocity vector acquired through the use of tracer techniques, such as PIV, is at the midpoint of the displacement vector. Thus, unless special care is taken, PIV data are also initially obtained on an irregular grid.
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- Fluid Mechanics