Abstract
The effect of void fraction on turbulent multifluid flows undergoing topology changes in a vertical channel is examined by numerical simulations using a front tracking and finite volume method. Several blobs or bubbles of the light fluid are initially placed in a turbulent channel flow. When the blobs collide and the liquid film between them becomes very thin it is ruptured, and the blobs are allowed to coalesce. The rupture is done for a predetermined film thickness selected in such a way that the results are relatively insensitive to its exact value. For the parameters used here, the blobs generally break up after the initial coalescence, and five simulations for void fractions from about 5% to 25% are carried out until the flow has reached an approximately steady state. The evolution of various integral quantities, such as the average flow rate, wall shear, and interface area, are monitored and compared. Various averages of the flow field and the phase distribution, over planes parallel to the walls, are then examined at late times, when the flow has reached an approximate statistically steady state. At steady state, the probability distribution of blob volumes is similar, and the light fluid is contained in blobs with an average Eötvös number of about 3.5, for all the void fractions. However, the deformation and the surface area of the largest blobs are much larger for the higher void fractions, suggesting that the flow starts to depart from the bubbly regime at a void fraction of about 15%.
8 More- Received 21 March 2019
DOI:https://doi.org/10.1103/PhysRevFluids.4.084301
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