Session: 04-01 Numerical and Data Based Methods for Multiphase Flows

Paper Number: 86898

86898 - Multiscale Euler-Lagrange Modeling of Bubble Collection and Phase Separation in a Vortex Chamber 

DynaSwirl free vortex gas-liquid separator is capable of efficiently and reliably separating gas-liquid mixtures in wide ranges of void fractions, flow rates, and levels of gravitational force for various applications. Numerical modeling and simulation of the two-phase flow in the separator complements experimentation and allows consideration of a much large range of the parameters than feasible without constructing and testing many separators. This provides needed information to understand the physics and to guide system design and operation optimization.

In this contribution we present an Eulerian-Lagrangian framework with geometric conversion to model the two-phase medium in the vortex flow, which integrates an Eulerian viscous mixture flow solver with a Discrete Singularity Model (DSM) for dispersed microbubbles. DSM simulates the bubble dynamics following the Rayleigh-Plesset-Keller-Herring equation and tracks their motions in a Lagrangian fashion, with Non-uniformities around the bubble accounted for using surface averaged quantities for the bubble dynamics. A two-way coupling between DSM bubbles and the continuum is realized through the local mixture density associated with the bubbles volume change and positioning. To take advantage of axisymmetric nature of overall mixture flow, Eulerian computational domain only considers a half central plane of the cylindrical separator. Extra steps were taken to rotate axisymmetric solution into full 3D for DSM computation, as well as to project averaged void fraction effects back onto the central plane after the three dimensional bubble distribution is known from DSM. Optimization of OpenMP shared-memory parallelization for the whole computation procedure was also conducted for further speedup purposes. In addition, as the bubbles grow and collect towards the vortex core which results in very high void fraction at core center and extremely large mixture density gradient at core edge the simulation encounters numerical instability issues. This is overcome by adopting a Gaussian smoothing void fraction scheme and adaptive time step size scheme.

Using this numerical tool, parametric study of phase separation effects are carried out. Comparison against experiments as well as cross-validation with other numerical method (such as transition of large DSM bubbles into level set cavities) will also be included and discussed.

Presenting Author: Jingsen Ma Dynaflow, Inc.