EXPERIMENTAL AND THEORETICAL STABILITY INVESTIGATIONS OF PLANE LIQUIDJETS

The present investigation has been undertaken in order to better under stand the development of free, plane liquid jets. Both the development of the basic laminar flow as well as its stability have been investig ated theoretically and experimentally. The velocity field and free sur face location of a liquid jet emanating from a plane channel was calcu lated numerically and the velocity and surface relaxation lengths were determined. Calculated velocity profile distributions were in good ag reement with Pitot tube measurements. Temporal linear stability calcul ations were performed using the calculated velocity distributions. The calculations showed five unstable modes, three sinuous and two dilata tional. Four of these modes have been reported earlier and one of the sinuous modes is considered to be 'new'. The linear stability calculat ions include surface tension as well as viscosity in the liquid and ga s. Hot wire anemometry measurements of controlled forced disturbances showed that waves in the experimental jet also were sinuous and that t he amplitude distribution was in fair agreement with theoretical resul ts. Shadowgraph visualisations showed the evolution of the waves on th e surface of the jet and it was found that the waves break up downstre am the nozzle. This break-up was visualized by particle visualisations , which showed that it creates strong streamwise streaks in the jet. ( C) Elsevier, Paris.