IMPROVEMENT OF EULER-EULER SIMULATION OF TWO-PHASE FLOW BY PARTICLE-CENTER-AVERAGED METHOD

Abstract

The standard Euler-Euler modelling is based on the phase-averaged method and the forces of the bubble are the function of gas volume fraction. However, the closure models for the forces are developed based on the measured bubble trajectory and the assumption that the forces act on bubble center. This inconsistency can lead to a nonphysical gas concentration in the center or in the near wall region of a pipe if the bubble diameter is larger than the mesh size. In addition, mesh independent solutions may not exist in these cases. In the present contribution, particle-center-averaged method is used in the average of the parameters for the disperse phase and the forces for bubble is changed to act on the bubble center. In this approach, the number density of the bubble centers is one of the solution variables. The gas volume fraction can be calculated from the number density by a diffusion-based method, which is much easier to implement in the CFD codes using the unstructured grids like OpenFOAM. A physically motivated model for the wall-contact force is introduced to ensure that the bubble centers cannot come arbitrarily close to walls. The remedy of the issues with the conventional phaseaveraged two-fluid model is demonstrated using a simplified two-dimensional test case. Furthermore, a comparison is made for pipe flow cases where experimental data are available. The results show that the particle-center-averaged method can help to decrease the over-prediction of the peaks in the gas volume fraction profiles and obtain the mesh independent solutions in the Euler-Euler modelling.