Defocusing digital particle image velocimetry and the three-dimensional characterization of two-phase flows
Defocusing digital particle image velocimetry (DDPIV) is the natural extension of planar PIV techniques to the third spatial dimension. In this paper we give details of the defocusing optical concept by which scalar and vector information can be retrieved within large volumes. The optical model and computational procedures are presented with the specific purpose of mapping the number density, the size distribution, the associated local void fraction and the velocity of bubbles or particles in two-phase flows. Every particle or bubble is characterized in terms of size and of spatial coordinates, used to compute a true three-component velocity field by spatial three-dimensional cross-correlation. The spatial resolution and uncertainty limits are established through numerical simulations. The performance of the DDPIV technique is established in terms of number density and void fraction. Finally, the velocity evaluation methodology, using the spatial cross-correlation technique, is described and discussed in terms of velocity accuracy.
© 2002 IOP Publishing Ltd Received 12 July 2001, in final form 14 February 2002, accepted for publication 1 March 2002, Published 28 March 2002, Print publication: Issue 5 (May 2002) The visit of Dr F Pereira to the CQV was made possible by a fellowship of the Funda¸c˜ao para a Ciˆencia e a Tecnologia, Portugal. The research was supported by the Office of Naval Research (contract N00014-97-1-0303), under the direction of Dr Ed P Rood and Dr Mark Hyman. The DDPIV technology is protected under a US pending patent filed by the California Institute of Technology.