Two-cell circulation in a liquid meniscus driven by a swirling gas jet.

A liquid issuing from a capillary needle adopts a cone-jet structure if the liquid is further driven by a coflowing gas jet. In the present work, flow patterns appearing in this cone-jet structure are studied by the volume-of-fluid numerical method. Axisymmetric motions of the liquid and gas, both treated as viscous incompressible fluids, are simulated. As the gas/liquid mass ratio increases, the meridional circulation develops in the meniscus region of the liquid flow. As the ratio exceeds a threshold, the flow becomes time periodic and droplet generating. Swirl, added in the gas jet, affects the liquid flow in two ways. First, the threshold value increases with swirl. Second, the circulation region transforms from the bubble-like into ring-like pattern and then becomes two-cellular. As swirl further increases, the cells separate, one cell disappears, and a new cell emerges being attached to the needle wall. The predicted metamorphoses of the flow topology might be important for atomization of a liquid fuel. [ABSTRACT FROM AUTHOR]