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.
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Received: 20 June 1999/Accepted: 27 November 2000
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Hirsa, A., Vogel, M. & Gayton, J. Digital particle velocimetry technique for free-surface boundary layer measurements: Application to vortex pair interactions. Experiments in Fluids 31, 127–139 (2001). https://doi.org/10.1007/s003480000266
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DOI: https://doi.org/10.1007/s003480000266