Study of a liquid-gas mixing layer: Shear instability and size of produced drops

International audienceWe study experimentally the atomization of a thick liquid film by a parallel gas flow, in order to understand the conditions of destabilization of the liquid film and the conditions of drop creation. We study in particular the regimes at low M (ratio of gas/liquid dynamic pressures), to test the scaling law proposed and validated in previous studies at large M (M=16M=16). The spatial inviscid stability analysis of the system is carried out with a new velocity profile taking into account the wake of the splitter plate (zero speed at the level of the splitter plate): the influence of liquid velocity on the shear instability frequency turns out to be significantly stronger for this type of velocity profile than for continuous profile. An asymptotic study of the dispersion relation leads to a new scaling law giving the wavenumber of the shear instability as a function of gas velocity UgUg, with a corrective term in M. Frequency measurements carried out by a spectral method show a good agreement with this corrected law. We investigate by way of optical probe measurements the size distribution of produced drops downstream. The difficulty of these measurements live in the decrease of the number density flux of drops at low M. Results obtained for the mean chord are consistent with previous studies. Diameter distributions are obtained from chord distributions with a numerical conversion procedure