[hwet]

The left picture is of velocity magnitude and the right one of tangential velocity in a cyclone body, i expect the tangential velocity contours to be the same as the velocity magnitude ones with just being a little lower in value but they appear to be different includin negative values as well, although the flow is all in one direction (clockwise). Can anyone tell where i am going wrong? maybe something to do with orientation?

[sutiut]

Hello Dear,
I have the same problem as you. I can not generate radial & tangentical velocity contours, right.
Could you?
please explain your method.
thanks,
Amir

[hwet]

i just plotted the vel mag, which seem right, the components i could not figure out, if you find a way let me know as well

[vasava]

Do you have any rotating frame of reference?

[hwet]

What do you mean by that? I tried to figure this rotating frame's meaning out but gave up... could you elaborate, and you can see what i mean from my pictures above...thanks

[ghost82]

Did you set correctly the rotation axis origin and direction in fluid panel?
Vasava was asking if you enabled the reference frame calculation in your simulation: if you don't know what it is, probably you didn't enable it.

[hwet]

Actually I did, and the contours above are those after setting the rotation axis, actually many people said that tangential velocity should be negative on one side and positive on the other but i kept on thinking they did not quite understand what i meant. do you guys personally think that the above contours are fine? or do you agree that the tangential velocity contours should be like vel magniude contours (positive)

[ghost82]

Sorry to be repetitive, but did you check if the rotation axis is coincident with the "vertical axis" of your cyclone? If the cyclone is centered in respect to the origin rotation axis is y or -y.
Moreover if you have multiple fluid zones make sure you setup the correct zone in the reference panel.

[hwet]

Thanks, I am going to do this again and get back to you. but also you do believe that the tangential vel contours are wrong and shouldnt be negative? I have seen many published research papers which plot them both positive and negative and i always suspect they are wrong...

[vasava]

I think ghost82 has given you all the hints you need. When you use reference frame the velocity and tangential velocity appear to be identical except that the magnitude are in inverse (Please remember that the absolute magnitude may not be the same). This is due to the fact the tangential velocity is relative to the axis of the rotating frame of reference. This is why if you plot tangential and relative tangential velocities they should be exactly the same.

[ghost82]

Originally Posted by hwet

Thanks, I am going to do this again and get back to you. but also you do believe that the tangential vel contours are wrong and shouldnt be negative? I have seen many published research papers which plot them both positive and negative and i always suspect they are wrong...

Yes, your tangential velocity contour is wrong: do not confuse x or z velocity (in your case) with tangential velocity.
See definition here of tangential velocity and how fluent handles it:
http://aerojet.engr.ucdavis.edu/flue...g/node1217.htm

If you look at the cylinder, taking into account the position of rotation axis the arrow indicating the tangential velocity has a positive sign (counterclockwise); opposite direction (clockwise) has negative sign.
If you define the axis with direction opposite to the axis indicated in that figure, the indicated arrow for tangential velocity will have negative sign (clockwise).

See some pictures I'm attaching for x,y and tangential velocity.

Daniele

[ghost82]

I see that you used cfd-post for post processing; by default tangential velocity is not available, so first you need to set rotation axis in cfd-post (define global rotation axis) and calculate velocity components (calculate velocity components), in "turbo" tab.
Then you can choose to plot the "Circumferential velocity" which is tangential velocity.
Otherwise plot your contours directly in fluent, by choosing tangential velocity.