Modelling Air Bubbles

fluidflow5 · May 25, 2017, 09:58

Hi,

I am looking to model air bubbles rising in water. Particularly, I would like to see the coalescence and break up of the bubbles. My simulation has gas entering at a speed of 0.001 m/s at the bottom of a water column. The issue I am having is that one bubble forms initially, and then following it is simply a stream of air.

I am running a transient scheme with a timestep of 0.001 [s]. Air is set to a dispersed fluid with water as a continuous fluid. I have turned on the free surface model with an interface compression level of 2. My turbulence is homogeneous and modelled by k-Epsilon.

For the fluid pair, I have set a surface tension coefficient of 0.072 N/m and a continuum surface force with water as the primary fluid. Interphase transfer is set to Particle Model. I have also chosen appropriate drag and non-drag forces for the model.

From my settings, can anyone spot a reason as to why this may be occurring? Any help is appreciated!

ghorrocks · May 25, 2017, 21:48

You appear to be modelling this using the free surface model? This is the most expensive type of multiphase model, but does allow you to model the detailed dynamics of the interface. Is this what you intend? Or can you do this with a simpler Eularian model?

There are zillions of studies of bubbles rising in water in the literature. I recommend you read a range of them to find out what approaches they have used.

Before the simulation you need to ensure that the configuration you intend to model is correct where you expect bubbles to form and not a jet. Also determine whether you expect to be in the spherical, spherical cap, or other bubble regimes as well.

After you have done this background work you are ready to start simulating. I will get onto that in a future post.

May 25, 2017, 09:58	Modelling Air Bubbles	#1
fluidflow5 New Member Join Date: May 2017 Posts: 1 Rep Power: 0	Hi, I am looking to model air bubbles rising in water. Particularly, I would like to see the coalescence and break up of the bubbles. My simulation has gas entering at a speed of 0.001 m/s at the bottom of a water column. The issue I am having is that one bubble forms initially, and then following it is simply a stream of air. I am running a transient scheme with a timestep of 0.001 [s]. Air is set to a dispersed fluid with water as a continuous fluid. I have turned on the free surface model with an interface compression level of 2. My turbulence is homogeneous and modelled by k-Epsilon. For the fluid pair, I have set a surface tension coefficient of 0.072 N/m and a continuum surface force with water as the primary fluid. Interphase transfer is set to Particle Model. I have also chosen appropriate drag and non-drag forces for the model. From my settings, can anyone spot a reason as to why this may be occurring? Any help is appreciated!

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May 25, 2017, 21:48		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	You appear to be modelling this using the free surface model? This is the most expensive type of multiphase model, but does allow you to model the detailed dynamics of the interface. Is this what you intend? Or can you do this with a simpler Eularian model? There are zillions of studies of bubbles rising in water in the literature. I recommend you read a range of them to find out what approaches they have used. Before the simulation you need to ensure that the configuration you intend to model is correct where you expect bubbles to form and not a jet. Also determine whether you expect to be in the spherical, spherical cap, or other bubble regimes as well. After you have done this background work you are ready to start simulating. I will get onto that in a future post.