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David April 20, 2004 12:25

angular velocity
 
Hello everyone:

I get a problem of how to get the angular velocity from the result file.I specified a rotation speed in the domain option,so I wanted to know how the speed change.In the cfx-post,I exported the velocity and found there are a lot of numbers,but no angular speed(whether is it only one?) All your advices would be appreciated

Regards

David

Glenn Horrocks April 20, 2004 18:13

Re: angular velocity
 
Hi David,

What do you want to do with the speed? You can extract the ccl file from your results file and that will have the speed, if you set it in the ccl file. Or is speed a function of something else so you need to extract it from the results as it is not known before the simulation?

Glenn

David April 20, 2004 22:03

Re: angular velocity
 
Hi Glenn,

Thanks for your advices. I want to konw how the rotation speed change after the solution.For example,I specified an angular velocity of 523.6 radiant s^-1 in the domain option.Does the speed chang to another? I am a new cfx user.I don't kown how to set the angular speed in the ccl file. Could you tell me how to set it and extract the ccl file from the results file?

Regards David

Glenn Horrocks April 21, 2004 18:20

Re: angular velocity
 
Hi David,

If you specify a constant angular rotation and what you want to do is extract what that speed was after the run there is a number of ways to do it.

Firstly - the ccl file is a text file describing what conditions to apply at the boundaries, the fluid properties, which fluid models to use etc. If you set up the run in CFX-Pre, by default the ccl file is incorporated at part of the def file and is not a seperate file. You can extract the ccl file from a def file if you want.

The easiest way to see what speed a results file used is to open the results file in CFX-Pre. Use the File/Import CCL option, and change the file type to definition/results file. You can then see the speed you used.

A second way for the script kiddies is to use a command line gizmo. Start a command line window from the CFX-Launcher, and type "cfx5cmds -read -definition [def or res file name] -text [output text file name]". It will then create a small text file which only contains the ccl, and the command giving the domain its rotational speed will be in there.

Regards, Glenn

gjy0775 April 21, 2004 21:57

Re: angular velocity
 
Hi Glenn:

Thank you very much for help. Your instructions were very helpful. I am afraid another problem comes out. When I tried "cfx5cmds -read -definition [def or res file name] -text [output text file name]" which you gave me.Both the def file and the res file got the same results.In my model,I specify a constant angular speed.Does it mean that the speed do not change after the running? But it was unreasonable.In a rotation domain, I set an angular speed of 523.6 radiant s^-1 and specified a cartesian velocityU=1 [m s^-1] V=0 W=0 in the inlet boundary condition.During the solution,the angular speed and the inlet boundary condition may interupt each other to get a zero net touque.So I think the angular speed may change after the solution finish. Hope you return.

Best regards! David


gjy0775 April 21, 2004 22:03

Re: angular velocity
 
Hi Glenn:

Thank you very much for help. Your instructions were very helpful. I am afraid another problem comes out. When I tried "cfx5cmds -read -definition [def or res file name] -text [output text file name]" which you gave me.Both the def file and the res file got the same results.In my model,I specify a constant angular speed.Does it mean that the speed do not change after the running? But it was unreasonable.In a rotation domain, I set an angular speed of 523.6 radiant s^-1 and specified a cartesian velocityU=1 [m s^-1] V=0 W=0 in the inlet boundary condition.During the solution,the angular speed and the inlet boundary condition may interupt each other to get a zero net touque.So I think the angular speed may change after the solution finish. How do I get the speed? Hope you return.

Best regards! David


roadkill April 21, 2004 23:26

Re: angular velocity
 
David,

I don't think you understand what the angular velocity is. Have you reviewed the documentation? The angular velocity specifies the speed at which the domain is rotating, thus the coriolis forces which are applied to the fluid. The velocity at the boundary does not have to be spinning with the domain.

Bottom line: if you specified an angular velocity, that's it! It doesn't change. If you really want to check it in Post, compare the Velocity at a wall (hybrid value) with the Velocity in the Stationary Frame at the same location (again, hybrid values). The difference will be equal to omega*r.

-RK

David April 22, 2004 10:02

Re: angular velocity
 
Hi roadkill: Thanks for your instuctions. Somebody tell me the angular velocity is the rotation velocity of the impeller.Is it right?

Thanks in advaced.

David

Glenn Horrocks April 22, 2004 18:29

Re: angular velocity
 
Hi David,

I agree with roadkill, you seem to have the fluid velocity and the rotational domain velocities mixed up. I recommend you have a look at the axial rotor/stator tutorial example in the documentation.

The rotational velocity sets up a rotating frame of reference for the domain it is applied to, such that the mesh moves with the frame of reference (assuming you are not using moving mesh, which is another option coming in CFX5.7). The fluid velocities are solved relative to the frame of reference - that is a node with zero velocity is actaully zero velocity relative to the rotating reference frame, and has a non-zero velocity (the velocity of the rotational frame at that point in fact) in the absolute frame frame of reference.

Regards, Glenn


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