Measurement by Free-Surface Synthetic Schlieren of the topography of a liquid interface

F. Moisy, M. Rabaud, K. Salsac

We have developed an optical method for the measurement of the instantaneous topography of the interface between two transparent fluids, named Free-Surface Synthetic Schlieren, or FS-SS (Moisy et al, 2009). This method is based on the analysis of the refracted image of a random dot pattern visualized through the interface. The apparent displacement field between the refracted image and a reference image obtained when the surface is flat is determined using a Digital Image Correlation algorithm. A numerical integration of this displacement field, based on a least square inversion of the gradient operator, is used for the reconstruction of the instantaneous surface height, allowing for an excellent spatial resolution with a low computational cost. The main limitation of the method, namely the ray crossing (caustics) due to strong curvature and/or large surface-pattern distance, is discussed.

A tutorial for implementing a FS-SS system under Windows is available here.

Fig 1 A plane wave generated by an oscillating plate.

Fig 2 Wake pattern generated by the translation of a small obstacle (comparison experiment / numerics).

Fig 3 Movie of the circular wave created by the impact of a drop (Acquisition rate 100 Hz).

Fig 4 Movie of the spreading of a silicon oil drop on a transparent substrate.

Publication

• Unpredictable tunneling of a classical wave-particle association
  A. Eddi, E. Fort, F. Moisy, Y. Couder, Phys. Rev. Lett. 102, 240401 (2009).
  [Abstract]
• A Synthetic Schlieren method for the measurement of the topography of a liquid interface
  F. Moisy, M. Rabaud, K. Salsac, Exp. in Fluids 46 (6), 1021-1036 (2009).
  [PDF]
• Measurement by Digital Image Correlation of the topography of a liquid interface
  F. Moisy, M. Rabaud, E. Pinsolle, ISFV13 - 13th International Symposium on Flow Visualization, and FLUVISU12 - 12th French Congress on Visualization in Fluid Mechanics, Paper #326, July 1-4, 2008, Nice (2008).
  [PDF]
• Optical measurement of ship waves by Digital Image Correlation
  M. Rabaud, F. Moisy, International Conference on Innovation in High Performance Sailing Yachts, 29-30 May 2008, Lorient, France, ISBN 978-1-905040-46-9e, pages 23-25 (2008).
  [PDF]
• Mesure de la déformation d’une surface libre par analyse du déplacement apparent d’un motif aléatoire de points
  M. Rabaud, F. Moisy and J. Rolland, Congrès Français de Mécanique (2007).
  [PDF]

Last modification: October 26 2009, 17:14:33.