Vortices in bubbly two-phase flow

The properties of a von Kármán vortex street are examined theoretically for bubbly flow around a rectangular obstacle. The time-dependent, two-dimensional Navier-Stokes equations describing each field are coupled through local pressure equilibration, a phenomenological momentum exchange term and a new representation of the virtual mass acceleration terms. Bubble fragmentation and coalescence are represented by the effect of relaxation to local Weber number equilibrium in a transport equation for the time and space variations of bubble-number density. Turbulence is represented by an eddy viscosity model. High-speed computer results for an air-water system agree well with published data for downstream gas accumulation in the vortices. Variations in Strouhal frequency with upstream void fraction are discussed in terms of bubble sublayer growth along the sides of the obstacle and the resulting movement of the flow separation streamline. Satellite eddy formation is observed, and the alteration of street characteristics by bubble migration is examined.