Simulating two fluids in zero gravity environment

siw · February 10, 2010, 11:47

Hi,

I have CFX v12.1 and may need to model a liquid flow from a reservoir (which once empty could have air replace the volume previously occupied by the liquid) in an accelerating/decelerating vehicle in a zero gravity environment. This is outside my usual area of expertise - atmospheric external aerodynamics.

Would CFX be able to simulate such a fluid flow?

Thanks.

ckleanth · February 10, 2010, 12:35

yes

.

siw · February 10, 2010, 13:44

ckleanth is this an area you have experience in? If so any words of wisdom.

ghorrocks · February 10, 2010, 17:44

It sounds like a standard free surface model, but one where the gravity vector is a function of time. This is only a trivial addition to a free surface model. It might get a bit more complicated if your space ship is rotating in addition to accelerating on occasion - then you need to consider whether a rotating frame of reference or moving mesh is required. But if not rotating then you can use a stationary mesh and it is not too complicated.

siw · February 11, 2010, 11:36

Thanks Glenn, is this something you've done before? I expect the vehicle motion to only be translation.

For free surface simulations are RANS adequate or does LES have to be used? And any thoughts on dealing with the mesh at the phase interface, especially if the interface is unsteady?

ghorrocks · February 11, 2010, 17:57

Free surface modelling can be done in either RANS or LES.

For free surface models make sure you have a high quality mesh near the interface, hexs if possible. Mesh refinement will resolve the interface better but if the interface moves you will probably have to do global refinement. Remeshing based on free surface motion is tricky in CFX.

ckleanth · February 12, 2010, 06:38

Quote:

Originally Posted by siw

ckleanth is this an area you have experience in? If so any words of wisdom.

sorry for late reply; no mate, have never modeled a zero gravity application but as Glenn said it shouldn't be any different to a standard free surface model. your ship movement should define the gravity vector however I'd think you'd need fine mesh throughout your domain

February 10, 2010, 11:47	Simulating two fluids in zero gravity environment	#1
siw Senior Member Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 742 Rep Power: 26	Hi, I have CFX v12.1 and may need to model a liquid flow from a reservoir (which once empty could have air replace the volume previously occupied by the liquid) in an accelerating/decelerating vehicle in a zero gravity environment. This is outside my usual area of expertise - atmospheric external aerodynamics. Would CFX be able to simulate such a fluid flow? Thanks.

February 10, 2010, 12:35		#2
ckleanth Senior Member George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 18	yes . __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

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February 10, 2010, 13:44		#3
siw Senior Member Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 742 Rep Power: 26	ckleanth is this an area you have experience in? If so any words of wisdom.

February 10, 2010, 17:44		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	It sounds like a standard free surface model, but one where the gravity vector is a function of time. This is only a trivial addition to a free surface model. It might get a bit more complicated if your space ship is rotating in addition to accelerating on occasion - then you need to consider whether a rotating frame of reference or moving mesh is required. But if not rotating then you can use a stationary mesh and it is not too complicated.

February 11, 2010, 11:36		#5
siw Senior Member Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 742 Rep Power: 26	Thanks Glenn, is this something you've done before? I expect the vehicle motion to only be translation. For free surface simulations are RANS adequate or does LES have to be used? And any thoughts on dealing with the mesh at the phase interface, especially if the interface is unsteady?

February 11, 2010, 17:57		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Free surface modelling can be done in either RANS or LES. For free surface models make sure you have a high quality mesh near the interface, hexs if possible. Mesh refinement will resolve the interface better but if the interface moves you will probably have to do global refinement. Remeshing based on free surface motion is tricky in CFX.