Université Paris-Sud

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   Accueil > Annuaire > C. Ruyer-Quil > resume-Kofman-280313

Complementary experimental and theoretical approaches to the investigation of three-dimensionality of falling film solitary waves

Nicolas Kofman, Sophie Mergui and Christian Ruyer-Quil (FAST)

We consider a liquid film falling down an inclined plane for moderate Reynolds number. Applying temporal forcing at the inlet, two-dimensional fast solitary waves are observed at low frequency. If the forcing frequency is higher, the waves are nearly sinusoidal ; these slow waves are unstable and evolve downstream into fast solitary waves as a result of a secondary instability. Starting from low-dimensional models, 2D stationary solutions are computed by continuation. Then, three-dimensional linear stability analysis is done with a pseudo-spectral Fortran code which has already been used for studying the stability of slow waves. We analyse the results by doing an energy budget in order to identify which terms are stabilizing or destabilizing. Two distinct modes are identified : a mainly driven capillary mode, which can be oscillatory and grows only in the capillary waves region, and an inertial mode, which slowly deforms the whole wave and disappears when the inclination angle is lower than 11 degrees. These theoretical predictions are put to the test by mean of comparison to experimental results. A Schlieren method is employed to visualize the wave patterns and measure the film height. We make a cartography of the 3D structures observed and compare the topography and wavelengths of the two modes of instability to numerical data.

Dernière modification : March 05 2013, 10:47:33.