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Dora June 24, 2010 15:48

Moment around and axis or on a plane
Hello everyone,
I'm trying to have the air tumble in a pipe calculated.
I placed a cylindrical coordinate system in the centre of the pipe and need the moment/torque around the Z axis. Through the X-Y planes of the coordinate system I also placed a plane (not shown on the pic). Then I tried to have the generate torque calculated on the plane which was unsuccessful. I then tried another approach. I have created a report --> moment with the parts chosen "out". Here the coordinate system laboratory is chosen which I cant change to cylindrical coordinate system which would probably give me the torque.

Can anyone help me to get use of on of the approaches I have taken please.

Thank you very much.
regards, CS


Vinicius June 24, 2010 16:35

Just copy the Z direction of your cylindrical coordinate system in the "Axis" field and set the origin in a Moment Report... Go to the Tools->Coordinate system and select your Coord. to get this information...

Dora June 25, 2010 15:24

Thank you for your reply. I have tried that and I get an result. Is there any way to cross check the result? The thing is I only get a torque if I chose an axis which is not on the centreline of the pipe. Currently Im having Z lying on the centreline. When I set in the report --> moment --> 0.0, 0.0, 1.0, it shows me 0.000Nm. When I switch to 1.0, 0.0, 0.0 I get some torque.

Thanks again

f-w June 25, 2010 16:43

Does your pipe geometry suggest you should be expecting any tumbling? It might help to plot in-plane (XY) velocities to see what's going on ...

Dora June 25, 2010 16:51

Yes it does. See the pic
I applied streamlines to see what is happening. As said earlier, around x and y it gives me a moment, not around Z which it should.
I have been struggling with this for quite some time. I could upload the file on a server if anyone would be free to check the setting.

regards, CS

f-w June 25, 2010 18:42

Are you running an inviscid simulation?

Dora June 26, 2010 07:46

Hi sure what is meant by that.
I'm running the "turbulent visocisty ratio" at 10, "turbulence intensity" at 0.05 a "No-Slip" wall conditions. I have the measured mass flow data and the CFD prediction is closer to the testing results when "No-Slip" is set. Pressure applied at the outlet is -2500Pa.

Vinicius June 26, 2010 08:41

Upload the file and I can take a look...

Dora June 26, 2010 08:51

Thats great. Please send me your email on and Ill give you the link.

Thanks again.

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