Influence of the wall boundary layer thickness on a gas jet injected into a liquid crossflow

The effects of the wall boundary layer thickness on the development of an axisymmetric gas jet injected into a confined vertical water flow were investigated. The variations in the wall boundary layer were made by using suction at the wall through rectangular profiled slots. The water velocity around the two-phase jet was studied for several boundary layer thickness values by laser Doppler velocimetry. The gas jet outline was extracted by image processing applied on visualisations for a wide variety of water, gas and suction conditions. These comparisons showed that the boundary layer has no influence on jet development. The data showed that the interactions between flows near the injection do not develop downstream, which accounts for the absence of the two classical contrarotating vortices in the medium field of the jet. The influence of the gas pocket, and then of buoyancy, is predominant over other phenomena. Received: 15 December 1999 / Accepted: 29 August 2000