Flow angle distribution

RPFigueiredo · April 22, 2013, 09:38

Hello again,

Would anyone happen to know how to produce a plot of flow angle? What I am tryuing to do is siumilar to this image I found in a research paper:

example.png

As you can see, this shows the flow angle in a constant-streamwise location.

Any ideas?

ghorrocks · April 22, 2013, 09:50

Define a variable in CFD-Post, and set it to the expression atan(Velocity U/VelocityV). Then draw this variable on a plane or whatever. You will have to change Velocity U and V to what ever direction you want to calculate the angle over.

RPFigueiredo · April 22, 2013, 09:59

Makes sense, thanks! I'll try that.

Is there a standard definition for the u, v and w components?

ghorrocks · April 22, 2013, 10:00

U=global X direction
V=global Y direction
W=global Z direction

RPFigueiredo · April 22, 2013, 10:10

So I guess VelocityU should be the tangential component and VelocityV should be the axial component to produce the angle I'm looking for. I couldn't, however, calculate the velocity components using the turbo tab (System Error: bad allocation / WARNING Action more_vars failed).

Is there some CEL command which could substitute those aforementioned components?

RPFigueiredo · April 22, 2013, 10:26

Also, I tried an approximation using atan(u/v) wich produced the following result:

angle.jpg

The values are fine, but there seems to be a very small region (pointed by the red arrow) where the angle diverges significantly. Is there a way I can adjust the legend so that I get lower range and therefore a better definition?

Never mind, just changed the max and min values on the contour plot itself!

ghorrocks · April 22, 2013, 19:21

No, U and V are not defined as axial and tangential. They are defined relative to the global axis - the little XYZ gizmo in the bottom right corner of your screen. How you align this to the axial and tangential directions for your model is up to you.

RPFigueiredo · April 23, 2013, 06:27

Yes, I know. I did that only to arrive at an approximate angle distribution to test if the method would work fine. My question is how do I get the tangential component, given the turbo tab cannot calculate it (for some reason...)!
The axial component is global Y, so that's no brainer!

ghorrocks · April 23, 2013, 08:31

Have a look in the CFX reference manual for the available CEL variables. There are variables for rotating frames of reference and cylindrical coordinate systems.

April 22, 2013, 09:38	Flow angle distribution	#1
RPFigueiredo Member Rolando Figueiredo Join Date: Mar 2013 Posts: 41 Rep Power: 13	Hello again, Would anyone happen to know how to produce a plot of flow angle? What I am tryuing to do is siumilar to this image I found in a research paper: example.png As you can see, this shows the flow angle in a constant-streamwise location. Any ideas?

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April 22, 2013, 09:50		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Define a variable in CFD-Post, and set it to the expression atan(Velocity U/VelocityV). Then draw this variable on a plane or whatever. You will have to change Velocity U and V to what ever direction you want to calculate the angle over.

April 22, 2013, 09:59		#3
RPFigueiredo Member Rolando Figueiredo Join Date: Mar 2013 Posts: 41 Rep Power: 13	Makes sense, thanks! I'll try that. Is there a standard definition for the u, v and w components?

April 22, 2013, 10:00		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	U=global X direction V=global Y direction W=global Z direction

April 22, 2013, 10:10		#5
RPFigueiredo Member Rolando Figueiredo Join Date: Mar 2013 Posts: 41 Rep Power: 13	So I guess VelocityU should be the tangential component and VelocityV should be the axial component to produce the angle I'm looking for. I couldn't, however, calculate the velocity components using the turbo tab (System Error: bad allocation / WARNING Action more_vars failed). Is there some CEL command which could substitute those aforementioned components?

April 22, 2013, 10:26		#6
RPFigueiredo Member Rolando Figueiredo Join Date: Mar 2013 Posts: 41 Rep Power: 13	Also, I tried an approximation using atan(u/v) wich produced the following result: angle.jpg The values are fine, but there seems to be a very small region (pointed by the red arrow) where the angle diverges significantly. Is there a way I can adjust the legend so that I get lower range and therefore a better definition? Never mind, just changed the max and min values on the contour plot itself!

April 22, 2013, 19:21		#7
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	No, U and V are not defined as axial and tangential. They are defined relative to the global axis - the little XYZ gizmo in the bottom right corner of your screen. How you align this to the axial and tangential directions for your model is up to you.

April 23, 2013, 06:27		#8
RPFigueiredo Member Rolando Figueiredo Join Date: Mar 2013 Posts: 41 Rep Power: 13	Yes, I know. I did that only to arrive at an approximate angle distribution to test if the method would work fine. My question is how do I get the tangential component, given the turbo tab cannot calculate it (for some reason...)! The axial component is global Y, so that's no brainer!

April 23, 2013, 08:31		#9
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Have a look in the CFX reference manual for the available CEL variables. There are variables for rotating frames of reference and cylindrical coordinate systems.