RIPPLES GENERATED ON A LIQUID-FILM AT HIGH GAS VELOCITIES

The growth of capillary ripples on a thin liquid film flowing concurrently with a high velocity gas flow is explored. In particular, a mechanism is examined whereby the ripples receive their energy from pressures and shear stresses exerted at the wave surface by the gas. The predicted wavelength of the most rapidly growing wave is found to be affected by system variables in the same manner as the measured distance between ripple crests. However, the magnitude of the predicted wavelength is one-half the observed wavelength. This could be explained by arguing that finite-amplitude two-dimensional waves are unstable to three-dimensional disturbances which cause alternate peaks and valleys along the crest of the original two-dimensional wave pattern.