Euler-Euler modelling of bubbly flow using particle-center-averaging method

The standard Euler-Euler two-fluid modelling is based on the phase averaging method and the bubble forces are functions of the gas volume fraction. Therefore, it is not guaranteed that all the gas belonging to the same bubble experiences the same force and moves with the same velocity. However, closure models for interfacial forces are typically developed based on the assumption that the bubbles’ motion can be represented by their center-of-mass on which the forces act. This inconsistency can lead to a nonphysical gas concentration in the center of a pipe or near its wall if the mesh size is smaller than the bubble diameter. In addition, a mesh independent solution may not exist in such simulations. In the present contribution, a particle-center-averaged method is used to average quantities related to the disperse phase such that the bubble forces act on the bubble centers. A systematic approach for the simulation of bubbly flows using the particle-center-averaged method is developed by combining the HZDR baseline closure models, a diffusion-based method for the field coupling and the Euler-Euler framework using the particle-center-averaged method. A physically motivated model for the wall-contact force is introduced to ensure that the bubble centers cannot come arbitrarily close to the walls. To validate this approach, a comparison is made with experimental data for monodisperse and fixed polydisperse bubbly flows in two different pipes. The results show that the particle-center-averaged method can alleviate the over-prediction of the peaks in the gas volume fraction profiles in the near wall region.