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Surface tracking in free-surface flows
Many multiphase flows consist of two or more immiscible phases that are separated by distinct large-scale surfaces (e.g. free-surface flows), rather than being distributed in droplets or bubbles.
Typical applications include the prediction of jet breakup, the motion of large bubbles in liquids, the motion of the liquid after a dam break, and the steady or transient tracking of any gas-liquid interface. In cases where the interface between the phases is of interest, it is possible to successfully model the flow using the free surface technique Volume-of-Fluid model (VOF) in ANSYS Fluent or the Free-Surface model in ANSYS CFX. Using free surface modeling, the CFD case can be reduced to a single set of momentum equations and continuity equation together with an equation for the volume fraction.
In the following example, a horizontal tube filled with 40% water and 60% air is at rest. The tube is then subject to a sinusoidal force that distorts the geometry. This will induce a wave that propagates back and forth through the tube. The VOF model keeps track of the surface. The simulation time is 10 seconds.
Dynamic meshing is used to deform the tube. More about dynamic meshing can be found here...