Three-component planar velocity measurements using Mach–Zehnder interferometric filter-based planar Doppler velocimetry (MZI-PDV)

Interferometric filter-based planar Doppler velocimetry is used in conjunction with imaging fibre bundles to make time-averaged three-component velocity measurements using a single imaging head. The Doppler frequency shifts of light scattered by particles entrained into the flow to be measured are transduced to intensity variations using a Mach–Zehnder interferometer. The free spectral range of the filter can be selected by adjusting the optical path difference of the interferometer. This allows the velocity measurement range, sensitivity and resolution to be varied. Three-component measurements are made possible by porting different views of the measurement plane to a single imaging head using the imaging fibre bundles. A comparison of three different image-processing techniques is presented and analysed with the aid of modelled images. Results are presented here for time-averaged measurements of a rotating disc with maximum velocities of ∼ ±34 m s−1 in the field of view with the computed measurement error in the orthogonal velocity components being (0.89, 0.68, 1.42) m s−1 for the measurement geometry used. Three-component velocity measurements were also made on a seeded air jet with a nozzle diameter of 20 mm and an exit velocity of ∼85 m s−1