Planar velocity visualization in high-speed wedge flow using Doppler Picture Velocimetry (DPV) compared with Particle Image Velocimetry (PIV)

Abstract

Ab ract : A technique for visualizing a velocity field in an entire plane has been developed by taking "Doppler Pictures" using Michelson interferometry. With the Doppler Picture Velocimetry (DPV), information about the instantaneous and local velocities of tracers passing through a light sheet is available. The technique for taking and processing the Doppler pictures has been improved recently and the state-of-the-art of the DPV method will be described with an application in high-speed fluid flows showing the velocity distribution in a light sheet plane crossing a supersonic wedge flow generated in the high-energy shock tunnel STB of ISL. A comparison with Particle Image Velocimetry (PIV) velocity visualizations is also presented. st

Mach–Zehnder interferometric filter based planar Doppler velocimetry (MZI-PDV)

“…The use of a Mach-Zehnder interferometer has several advantages over molecular filters, the choice of illumination laser is no longer limited by the availability of a suitable absorption line and the path length imbalance of the interferometer can be selected to correspond to the expected velocity range for a given situation. Michelson interferometers have previously been used to make planar single component velocity measurements [5,6]. However the Mach-Zehnder interferometer offers the advantage of providing two complementary outputs allowing the scattered light intensity to be normalized by taking the difference of the two outputs divided by the sum potentially increasing the sensitivity of the system.…”

Optical fibre laser velocimetry: a review

“…The filter used can be interferometric [125][126][127] or an atomic or molecular absorption filter [24,35,128,129]. Although some work has been done using focused beams for illumination and making single point measurements [130], the main advantage of using an optical filter over other methods is the ability to measure multiple points simultaneously.…”

Full-field interferometry using infinity corrected optics

“…These interferometry objectives have a built-in beam splitter to divide the illumination and provide a reference, and as such they do not allow self-mixing configurations where the light from the object plane is mixed with itself. For example, such selfmixing configurations have been used in areas such as flow visualisation [3] and quantitative flow measurements [4][5][6][7], where the illumination is provided in the form of a laser light sheet and a path length imbalanced interferometer is used as an optical filter to resolve Doppler frequency shifts, and in speckle shearing interferometry [8][9][10] where the speckle pattern from an illuminated test object is mixed with an offset version of itself. In both of these applications the light collected from the object plane is divided into the two arms of the interferometer before being recombined and the resulting interference pattern recorded.…”

“…Such a set-up can be used; with a single imaging lens [4,11], for endoscopic measurements [12], or to port multiple images from imaging fibre bundles allowing spatially multiplexed measurements [5]. As such the use of infinity-corrected optical systems have great potential in full-field interferometry for many applications in optical instrumentation, including vibration and strain measurement [9,10], flow field visualisations [3] and quantitative velocity measurements [4][5][6][7].…”