A particle-center-averaged Euler-Euler model for monodisperse bubbly flows


A particle-center-averaged Euler-Euler model for monodisperse bubbly flows

Lyu, H.; Lucas, D.; Rzehak, R.; Schlegel, F.

The standard Euler-Euler model is based on the phase-averaging method. Each bubble force is a function of the local gas volume fraction. As a result, the coherent motion of each bubble as a whole is not enforced when the bubble diameter is larger than the mesh size. However, the bubble force models are typically developed by tracking the bubbles' centers of mass and assuming that the forces act on these locations. In simulations, this inconsistency can lead to a nonphysical gas concentration in the center or near the wall of a pipe when the bubble diameter is larger than the mesh size. Besides, a mesh independent solution may not exist in such cases.

In the present contribution, a particle-center-averaging method is used to average the solution variables for the disperse phase, which allows to represent the bubble forces as forces that act on the bubbles' centers of mass. An approach to simulate bubbly flows is formed by combining the Euler-Euler model framework using the particle-center-averaging method and a diffusion-based method that relates phase-averaged and particle-center-averaged quantities. The remediation of the inconsistency with the standard Euler-Euler model based on phase-averaging method is demonstrated using a simplified two-dimensional test case. The test results illustrate that the particle-center-averaging method can alleviate the over-prediction of the gas volume fraction peak in the channel center and provide mesh independent solutions. Furthermore, a comparison of both approaches is shown for several bubbly pipe flow cases where experimental data are available. The results show that the particle-center-averaging method can alleviate the over-prediction of the gas volume fraction peaks in the wall peaking cases as well.

Keywords: particle-center-averaging; phase-averaging; bubble number density; diffusion equation; wall-contact force model; multiphase flow; Euler-Euler model

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Permalink: https://www.hzdr.de/publications/Publ-32958
Publ.-Id: 32958