SNAKES AND CORKSCREWS IN CORE-ANNULAR DOWN-FLOW OF 2 FLUIDS

Core-annular flow of two fluids is examined at the onset of a non-axis ymmetric instability. This is a pattern selection problem: the bifurca ting solutions are travelling waves and standing waves. The former tra vel in the azimuthal direction as well as the axial direction and woul d be observed as corkscrew waves. The standing waves travel in the axi al direction but not in the azimuthal direction and appear as snakes. Weakly nonlinear interactions are studied to see whether one of these waves will be stable to small-amplitude perturbations. Sample situatio ns for down-flow are discussed. The corkscrews tend to be preferred wh en the annulus is narrow, while snakes are more likely when the annulu s is wide.