Digital particle velocimetry technique for free-surface boundary layer measurements: Application to vortex pair interactions |
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Authors: | A H Hirsa M J Vogel J D Gayton |
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Institution: | (1) Department of Mechanical Engineering, Aeronautical Engineering and Mechanics, Rensselaer Polytechnic Institute Troy, NY 12180-3590, USA (hirsaa@rpi.edu), US |
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Abstract: | A variation of the digital particle image velocimetry (DPIV) technique was developed for the measurement of velocity at a
free surface for low Froude number flows. The two-step process involves first determining the location of the free surface
in the digital images of the seeded flow using the fast Fourier transform-based method of surface elevation mapping (SEM),
which takes advantage of total internal reflection at the interface. The boundary-fitted DPIV code positions the interrogation
windows below the computed location of the interface to allow for extrapolation of interfacial velocities. This technique
was designed specifically to handle large surface-parallel vorticity which can occur when the Reynolds number is large and
surface-active materials are present. The SEM technique was verified on capillary-gravity waves and the full boundary-fitted
DPIV technique was applied to the interaction of vortex pairs with a free surface covered by an insoluble monolayer. The local
rise and fall of the free surface as well as the passage and return of a contamination front was clearly observed in the DPIV
data.
Received: 20 June 1999/Accepted: 27 November 2000 |
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