Simulation Of Rising Bubble Research Articles

An incompressible–compressible Lagrangian particle method for bubble flows with a sharp density jump and boiling phase change

Modeling the boiling phase change is particularly challenging for Lagrangian particle methods due to a high density ratio and dramatic volume expansion. In this study, the incompressible moving particle semi-implicit (MPS) method and the weakly compressible smoothed particle hydrodynamics (SPH) method are coupled to develop an incompressible–compressible particle method for modeling a multiphase flow with boiling. The coupling strategies developed by Lind et al. (JCP, 2016) are adopted. A high speed of sound must be employed in SPH for incompressible bubbles in a heavy liquid under gravity, which can cause severe spurious pressure fluctuations. In this situation, a technique for detecting bubble connectivity is developed to average the pressure inside each bubble for stable coupling. This pressure averaging strategy is physically consistent due to the high density ratio. Because the pressure coupling strategy tends to break the force balance between the surface tension and the pressure jump across the interface, the surface tension model must be based only on the liquid particles near the interface. The boiling mass transfer is modeled in a straightforward manner by injecting gas particles towards the gas phase from the liquid interface particles. The gas volume expansion is naturally considered by the coupling method, as the gas particle distribution can be automatically regulated in the SPH calculation. Rising bubble simulations with different surface tension coefficients and density ratios verify the proposed method for a bubble flow. The Stefan and sucking problems as well as a horizontal film boiling flow are simulated to verify the boiling model and to demonstrate its straightforward capability to handle gas volume expansion.

Comparison of Surface Tension Models for the Volume of Fluid Method

With the increasing use of Computational Fluid Dynamics to investigate multiphase flow scenarios, modelling surface tension effects has been a topic of active research. A well known associated problem is the generation of spurious velocities (or currents), arising due to inaccuracies in calculations of the surface tension force. These spurious currents cause nonphysical flows which can adversely affect the predictive capability of these simulations. In this paper, we implement the Continuum Surface Force (CSF), Smoothed CSF and Sharp Surface Force (SSF) models in OpenFOAM. The models were validated for various multiphase flow scenarios for Capillary numbers of 10 − 3 –10. All the surface tension models provide reasonable agreement with benchmarking data for rising bubble simulations. Both CSF and SSF models successfully predicted the capillary rise between two parallel plates, but Smoothed CSF could not provide reliable results. The evolution of spurious current were studied for millimetre-sized stationary bubbles. The results shows that SSF and CSF models generate the least and most spurious currents, respectively. We also show that maximum time step, mesh resolution and the under-relaxation factor used in the simulations affect the magnitude of spurious currents.

Benchmark computations for 3D two-phase flows: A coupled lattice Boltzmann-level set study

Following our previous work on the application of the diffuse interface coupled lattice Boltzmann-level set (LB-LS) approach to benchmark computations for 2D rising bubble simulations, this paper investigates the performance of the coupled scheme in 3D two-phase flows. In particular, the use of different lattice stencils, e.g., D3Q15, D3Q19 and D3Q27 is studied and the results for 3D rising bubble simulations are compared with regard to isotropy and accuracy against those obtained by finite element and finite difference solutions of the Navier–Stokes equations. It is shown that the method can eventually recover the benchmark solutions, provided that the interface region is aptly refined by the underlying lattice. Following the benchmark simulations, the application of the method in solving other numerically subtle problems, e.g., binary droplet collision and droplet splashing on wet surface under high Re and We numbers is presented. Moreover, implementations on general purpose GPUs are pursued, where the computations are adaptively refined around the critical parts of the flow.

GPGPU-based rising bubble simulations using a MRT lattice Boltzmann method coupled with level set interface capturing

A multiphase Lattice Boltzmann (LB) scheme coupled with a level set interface capturing model is used for the simulation of multiphase flows, and in particular, rising bubbles under moderate and high density and viscosity ratios. We make use of consistent time integration and force discretization schemes in particular for pressure forces along with using multiple relaxation time (MRT) form of the collision in the LB equation which enables us to preserve stability and accuracy for high density and critical Eo numbers. We first present the solution for the standard test of a static bubble in order to show the accuracy of the solution with respect to the Laplace law for pressure and also the spurious velocity level. We present quantitative benchmark computations and error analysis for the 2D rising bubble test cases being further validated against high precision finite element solutions in Hysing et al. (2009). Furthermore, by applying efficient multi-core and many core general purpose GPU (GPGPU) implementations outlines, we demonstrate that the desired parallel scaling characteristics of general LBM solutions are well preserved for the proposed coupled computations. The presented implementations are shown to outperform the available GPU-based phase-field LBM solvers in terms of computational time, turning the scheme into a desirable choice for massive multiphase simulations in three dimensions.

Simulation of expanding bubble through a hole in a channel driven by pressure using lattice Boltzmann method

The behavior of expanding bubble motion through a hole in a channel driven by pressure is studied using lattice Boltzmann method. The multiple-relaxation-time scheme and the pseudo-potential model with discretized force treatment are used to obtain higher numerical stability. The rising bubble simulations are carried out to validate the algorithm as being suitable for simulating bubble dynamics. Then the simulation of expanding bubble through a hole in a channel driven by pressure is presented. The dynamic process of expanding bubble is revealed through the change of bubble size and the deformation of bubble shape during it flowing along the channel. Moreover, to further investigate expanding bubble behavior, comparisons are conducted for it under different driving pressures, bubble sizes, bubble viscosities.

Rising bubble simulations using lattice Boltzmann method coupled with level set interface capturing

AbstractA multiphase Lattice Boltzmann (LB) scheme coupled with a level set interface capturing module is used for the simulation of multiphase flows, and in particular, rising bubbles under moderate and high density and viscosity ratios. We employ a consistent, robust discretization of the pressure forces which enables us to preserve stability and accuracy. The accuracy of the present scheme is shown to be competitive with that of the benchmark data from the finite element solutions in [3]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A fully adaptive front tracking method for the simulation of two phase flows

This work presents a computational methodology for the simulation of three-dimensional, two-phase flows, based on adaptive strategies for space discretization, as well as a varying time-step approach. The method is based on the Front-Tracking method and the discretization of the Eulerian domain employs a Structured Adaptive Mesh Refinement strategy along with an implicit–explicit pressure correction scheme. Modelling of the Lagrangian interface was carried out with the GNU Triangulated Surface (GTS) library, which greatly reduced the difficulties of interface handling in 3D. The methodology was applied to a series of rising bubble simulations and validated employing experimental results and compared to literature numerics. Finally, the algorithm was applied to the simulation of two cases of bubbles rising in the wobbling regime. The use of adaptive mesh refinement strategies led to physically insightful results, which otherwise would not be possible in a serial code with a uniform mesh.