ANSYS CFX Tutorial 7

January 6, 2009, 19:32

Hi,

I am working through the tutorials ad have come to tute 7 whihc is the free surface flow over a 2d bump. This tutorial is very applicable to what i would liek to do my thesis on.

When I try to solve the problem I get an error message which reads, "The density-difference buoyancy model is being used, but the buoyancy reference density has not been specified"

I have tried loading the session file supplied but it also comes up with the error when I try to solve it

Has anyone had a similar problem or any advice on how to resolve the problem?

Regards,

Sam

January 7, 2009, 07:29

I did some meshes of this case. IF YOU WANT TO use these grids...

http://www.4shared.com/file/65772301..._Mr_Brito.html

http://www.4shared.com/file/65770211..._Mr_Brito.html

January 7, 2009, 17:03

Thayou I will have a play,

I am very much learning CFD and know quite little about the topic at this stage, I have read a few books Do you know of any other ways to better understand using CFD to generate free surface flows?

I feel the problem may be in the setting up of my problem rather than the meshing but I will try again.

Thanks again,

Sam

January 7, 2009, 18:34

Hi,

I agree the problem likely to be the setup, not the mesh. The error message refers to the buoyancy reference density - have you set it as it requests?

What version of CFX are you using?

Glenn Horrocks

January 7, 2009, 19:03

I am currently using v11

I am about to have been reading CFX help

"For a flow containing a continuous phase and a dilute dispersed phase, you should set the buoyancy reference density to that of the continuous phase"

My understanding is that the reference density should be that of the water. Do you believe this is correct?

Regards,

Sam

January 8, 2009, 17:23

Hi,

Yes, you are correct.

Glenn Horrocks

January 15, 2009, 08:10

Did you select both "Air at 25C" and "Water" in the fluid list when defining the domain?

January 24, 2009, 20:48

Hi Sam,

Besides what Peter said, you should also set density reference (under gravity force vectors) as the one of the lighter fluid.

In The density difference model only the heavier fluid suffers the gravity force.

See at Help how this model works.

hope was helpful

January 6, 2009, 19:32	ANSYS CFX Tutorial 7	#1
Sam Guest Posts: n/a	Hi, I am working through the tutorials ad have come to tute 7 whihc is the free surface flow over a 2d bump. This tutorial is very applicable to what i would liek to do my thesis on. When I try to solve the problem I get an error message which reads, "The density-difference buoyancy model is being used, but the buoyancy reference density has not been specified" I have tried loading the session file supplied but it also comes up with the error when I try to solve it Has anyone had a similar problem or any advice on how to resolve the problem? Regards, Sam

January 7, 2009, 07:29	Re: ANSYS CFX Tutorial 7	#2
Rogerio Fernandes Brito Guest Posts: n/a	I did some meshes of this case. IF YOU WANT TO use these grids... http://www.4shared.com/file/65772301..._Mr_Brito.html http://www.4shared.com/file/65770211..._Mr_Brito.html

January 7, 2009, 17:03	Re: ANSYS CFX Tutorial 7	#3
Sam Guest Posts: n/a	Thayou I will have a play, I am very much learning CFD and know quite little about the topic at this stage, I have read a few books Do you know of any other ways to better understand using CFD to generate free surface flows? I feel the problem may be in the setting up of my problem rather than the meshing but I will try again. Thanks again, Sam

January 7, 2009, 18:34	Re: ANSYS CFX Tutorial 7	#4
Glenn Horrocks Guest Posts: n/a	Hi, I agree the problem likely to be the setup, not the mesh. The error message refers to the buoyancy reference density - have you set it as it requests? What version of CFX are you using? Glenn Horrocks

January 7, 2009, 19:03	Re: ANSYS CFX Tutorial 7	#5
Sam Guest Posts: n/a	I am currently using v11 I am about to have been reading CFX help "For a flow containing a continuous phase and a dilute dispersed phase, you should set the buoyancy reference density to that of the continuous phase" My understanding is that the reference density should be that of the water. Do you believe this is correct? Regards, Sam

January 8, 2009, 17:23	Re: ANSYS CFX Tutorial 7	#6
Glenn Horrocks Guest Posts: n/a	Hi, Yes, you are correct. Glenn Horrocks

January 15, 2009, 08:10	Re: ANSYS CFX Tutorial 7	#7
Peter Guest Posts: n/a	Did you select both "Air at 25C" and "Water" in the fluid list when defining the domain?

January 24, 2009, 20:48	Re: ANSYS CFX Tutorial 7	#8
Leandro Resende Guest Posts: n/a	Hi Sam, Besides what Peter said, you should also set density reference (under gravity force vectors) as the one of the lighter fluid. In The density difference model only the heavier fluid suffers the gravity force. See at Help how this model works. hope was helpful

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