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A P.I.V. Processing Technique for Directly Measuring Surface-Normal Velocity Gradient at a Free Surface

[+] Author Affiliations
Tuy N. M. Phan, Chuong V. Nguyen, John C. Wells

Ritsumeikan University, Kusatsu, Shiga, Japan

Paper No. FEDSM2005-77493, pp. 299-303; 5 pages
  • ASME 2005 Fluids Engineering Division Summer Meeting
  • Volume 2: Fora
  • Houston, Texas, USA, June 19–23, 2005
  • Conference Sponsors: Fluids Engineering Division
  • ISBN: 0-7918-4199-5 | eISBN: 0-7918-3760-2
  • Copyright © 2005 by ASME


Compressive surface-normal velocity gradient at a free surface leads to high mass transfer across a free surface. Our research aims to directly measure this velocity gradient at the free surface by proposing an advanced Particle Image Velocimetry (PIV) technique and simultaneously evaluate its applicability. This technique, PIV/IG (Interface Gradiometry), was proposed by Nguyen et al. (2004) to directly measure wall velocity gradient with high S.N.R. Herein, we adapt this technique to measure the compressive surface-normal velocity gradient at the free surface of open channel flow with minimal fluctuation of water surface. We validate this technique in a two-component PIV configuration by synthetic PIV images corresponding to uniform compression, linearly-varying compression, and a velocity field based on DNS data of open channel flow at friction Reynolds number Reτ = 240 and zero Froude number. The results clearly show that this technique works much better than the velocity differentiation method. The effect of template size on the measured value is evaluated.

Copyright © 2005 by ASME



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