A boundary element method for calculating the shape and velocity of two-dimensional long bubble in stagnant and flowing liquid

A numerical method based on a boundary element method (BEM) has been developed for computing the velocity and the shape of long bubbles moving steadily in stagnant and flowing liquid in 2D case: plane and axisymmetrical. The flow is assumed to be inviscid and incompressible. The method consists in solving simultaneously a Poisson equation characterizing the flow and an equation for bubble shape in the form of a functional-differential equation resulting from both Bernoulli equation and the jump conditions at the interface. The Poisson equation is solved by a BEM with an iterative loop for nonlinear source term while the system of nonlinear algebraic equations obtained by discretizing the equation on the interface is solved by the Powell's hybrid algorithm. The bubble shape and velocity are obtained as a part of the solution. The problem of multiple solutions is investigated numerically and the maximum velocity criterion is used for selecting the physical solution. The results obtained by the simulation are in good agreement with the experimental and numerical results of previous studies.