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-   -   Contour plot with negative velocity (http://www.cfd-online.com/Forums/cfx/26598-contour-plot-negative-velocity.html)

J October 30, 2008 16:08

Contour plot with negative velocity
 
Hello hello! I am writing again for the same problem...CFX-Post is not plotting the negative values of the velocity. Consider a plane and you want to create a contour plot on this plane...in some region the velocity is positive and in other regions the velocity is negative...I dunno why but there is no way to say to CFX-Post to plot the negative values of the velocity and show also in the legend the negative values...it is just plotting the positive values cutting the negative...I've done everything...global, local, user defined...no way...doesn't work. Do you have any idea?? I'm going crazy with this stupid problem... PS: I am using the components of the velocity...not the magnitude, so I should see when the velocity is positive and when is negative. Thanks

J

CycLone October 31, 2008 09:28

Re: Contour plot with negative velocity
 
If there are negative values, Post will plot them. What are the ranges of velocity for each component (hint, go to the variables tab and select a variable to see it's range).

Post does not have a problem with this, so you must be doing something wrong.

-CycLone

J October 31, 2008 12:28

Re: Contour plot with negative velocity
 
The range is -0.0404405 / 0.0477998. For plotting I create a plane, I creat a contour on that plane and I put Velocity w as variable. I tried with global range, local, user defined etc etc...but is not working... Any suggestions?

J

CycLone October 31, 2008 13:48

Re: Contour plot with negative velocity
 
Are you sure you have negative velocity in the Z direction? If the local range doesn't show it, then you must not have negative velocities at that plane location. Post just plots what is there, so there is no reason it wouldn't show it.

Try creating an isosurface of "Velocity w" equal to zero (use conservative, not hybrid values). This will show you where velocity is negative.

-CycLone

J October 31, 2008 14:44

Re: Contour plot with negative velocity
 
Of course I have a negative velocity at that plane!

CycLone October 31, 2008 14:51

Re: Contour plot with negative velocity
 
If Post doesn't show negative velocities, how do you know you it is negative at that location?

J October 31, 2008 15:15

Re: Contour plot with negative velocity
 
Because I exported the data and there are negative values...And the main flow is going in the -Z direction, so...

CycLone November 3, 2008 17:11

Re: Contour plot with negative velocity
 
You exported the data at the plane where you are locating your contour?

J November 3, 2008 17:23

Re: Contour plot with negative velocity
 
Yes...I've done the contour in Tecplot and works perfectly...

CycLone November 3, 2008 17:31

Re: Contour plot with negative velocity
 
So, to get this straight. At the plane of interest flow is moving in the negative x direction at some locations. If you create a plane at this location and plot Velocity u, Post does not plot any negative velocities?

I find it very difficult to believe this is the case; there must be something you have done or interpreted wrong. There is no reason Post would modify the results or otherwise display them differently.

Have you sent you results and state file to ANSYS technical support for advice? Can you post them on an ftp site for forum users to view?

-CycLone

J November 3, 2008 17:38

Re: Contour plot with negative velocity
 
Believe me...this is the case...Post is cutting the negative values...since I think, after this discussion, that there is a problem in Post I will send that to our technical support. As soon as I can I will let you know the answer, in this post or in another one but always with the same name "Contour plot with negative velocity". Honestly...I am not a stupid :) Post is doing something strange...

CycLone November 3, 2008 17:46

Re: Contour plot with negative velocity
 
Hi J,

I don't think you're stupid; I just can't comprehend how this could occur. If the files are small enough, you can email them to me at cyclone_cfd@hotmail.com.

-CycLone


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