Finite element analysis of bubbly flow around an oscillating square-section cylinder

The bubbly flow around a square-section cylinder, which is forced to oscillate normal to a uniform flow, is simulated by an incompressible two-fluid model. The model is solved by the Arbitrary Lagrangian-Eulerian (ALE) finite element method. The width of the cylinder is 30 mm. A bubbly flow is assumed, and the bubble diameter is set as 1 mm. The volumetric fraction of the gas-phase upstream of the cylinder is 0.05, where the Reynolds number defined by the volumetric velocity of the liquid-phase is 200. With an increment in the cylinder oscillation frequency Sc, the vortex shedding frequency St approaches the Sc value. When the Sc is increased beyond a critical value, the lock-in occurs, in which the vortex shedding is synchronized with the cylinder oscillation. The time-averaged drag coefficient and the root-mean-square of the lift coefficient for the cylinder take their maximum values at the lock-in state. The volumetric fraction of the gas-phase alpha(g) is higher in the wake of the cylinder, irrespective of the Sc value. The alpha(g) value is lower below the lock-in state and higher in the lock-in state than the value for the stationary cylinder. (C) 2002 Elsevier Science B.V. All rights reserved.