A new approach to flow-field measurement - A view of Doppler global velocimetry techniques

Nonintrusive techniques for determining velocities in fluid flowfields, based on the use of laser technology, have been the subject of much research over the last three decades. Many of these techniques, such as laser-Doppler-anemometry (LDA) and laser-two-focus-anemometry (L2F), have been based on point-wise measurements until the advent, in the last decade, of particle image velocimetry (PIV). There is much interest in pursuing the goal of nonintrusive, whole-field velocity measurements, although such techniques are still some way from maturity. A new technique has recently emerged to challenge the position of PIV: the technique of Doppler global velocimetry (DGV). This paper outlines the origins of the technique, the physical principles involved, and the potential advantages of DGV over PIV. A review is made of the technology used by the small number of groups researching this new method, drawing comparisons between the major aspects of their differing techniques. Finally, examples are given of ''test case'' measurements of two well-established velocity fields: those of a rotating disc, and those in a subsonic open jet. (C) 1997 by Elsevier Science Inc.