Affiliations: Nuclear Engineering Research Laboratory, University of
Tokyo, Tokai-mura, Ibaraki 319-1106, Japan.
Abstract: In Particle Image Velocimetry (PIV), the cross correlation tracking
technique is widely used to analyze the particle images. The technique assumes
that the fluid motion, within small regions of the flow field, is given by
parallel movements over short time intervals. However, actual flow fields may
have some distorted motion,such as rotation and shear. Therefore, if the
distortion of the flow field is not negligible, the fluid motion can not be
tracked well using the cross correlation technique. The author proposed a new
particle tracking technique, based on the particle cluster matching using
linear Affine Transformation. The algorithm can be applied to flow fields which
exhibit character-istics such as rotation and shear. The deformation of the
cluster pattern is expressed by the linear Affine Transformation. The parameter
of the transformation can be determined using the least square technique from
the particle positions. The effectiveness of the tracking techniques, including
3D cross correlation, Spring Model and Affine Transformation, were evaluated
with synthetic data of three-dimensional flow field. The cross correlation
technique could be applicable to the small deformation cases. When the
deformation of parti-cle pattern between two images are very large, the pattern
deformation could not be expressed by the Affine Transformation, i.e., linear
transformation, resulting in mis-tracking. However, the Spring Model technique
was found to be more effective even in the larger deformation condition,
because the Spring Model does not assume the linear transformation.
