Doppler global velocimetry - Fundamentals, implementation and selected applications

Abstract

Doppler global velocimetry (DGV) – also known as planar Doppler velocimetry (PDV) – is a relatively new technique capable of obtaining planar velocity maps of flow fields. Although its original proposal dates back to a patent by Komine of Northrop Corporation in 1990, it has found use in a rather limited range of applications with only a limited number of research institutes world-wide actively developing or frequently using the technique. Dr. J. Meyers of NASA Langley not only gave the new technique the name ‘DGV’ but more importantly was among the first to turn the rather simple concept behind DGV into a functional tool for use in applied aerodynamics. There are several reasons for the rather limited use of DGV more than one decade since introduction. One of the foremost factors has been the rapid development of the particle image velocimetry technique (PIV) which has taken benefit from significant advances in laser and camera technology as well as from increased computing power. To date PIV has made planar flow mapping possible in nearly in any application involving fluid mechanics. Another hurdle faced by DGV is that it requires a considerable amount of background knowledge and specialized hardware to arrive at a functional DGV system. Contrary to PIV, which measures the displacement of particle images, DGV relies on a quantitative measurement of light intensity which effectively makes it an analogue technique (similar to measuring a voltage or temperature). Background scene illumination is just one of many factors which can severely impair a DGV measurement while a PIV system under the same conditions would operate without any significant loss of signal. In spite of these and other disadvantages DGV holds promises in areas that are beyond the reach of PIV. The article first gives an overview of the main principles on which DGV is founded, followed by some exemplary applications of the DGV technique.