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-   -   Plotting backflow on a mass flow graph (two way FSI) (http://www.cfd-online.com/Forums/cfx/68470-plotting-backflow-mass-flow-graph-two-way-fsi.html)

Cirion0000 September 21, 2009 11:34

Plotting backflow on a mass flow graph (two way FSI)
 
Hi, I'm trying to figure out how to show the backflow on a graph, considered as "negative" flow. When I plot a graph using the expression Rho * Average Velocity * Cross-sectional area, I get a plot that is pretty reasonable and expected (a sinusoidal wave [my input pressure is sinusoidal]) but it never crosses below the X axis. I know this is wrong because you can see from the animations that flow comes back into the device as well. Is there a way to get CFX to properly plot this? I would try using the MassFlow expression but I get errors using this (so I had to improvise with the Rho*Avg. Velocity*Cross-sectional area)

Also, is there a way to plot the overlay/summation of two locations at once? (There are essentially two openings for outlet/inlet)

ghorrocks September 21, 2009 18:30

The MassFlow function works fine for backflow. The problem is more likely to be that you are using an inlet as your boundary condition and that does not allow backflow. Try using an opening instead.

Cirion0000 September 28, 2009 12:16

I did use the BC "opening" in CFX-pre. And I can visually inspect, and there is definitely backflow in the vector plot.

Also, the massflow command does work, but only for the final timestep (so it is working... sort of), which does not make sense. Otherwise, it gives me this error:

"WARNING
Unable to calculate mass flow the surface.
Some or all of the required variables are not present:
Density, Velocity, and, for multi-phase cases, Volume Fraction."

And just to clarify again the solution makes sense. The vector profile and deflection behave as expected. I'm just not entering the right expression, or something.

ckleanth September 28, 2009 13:41

if you haven't asked to save the requested variable at a particular timestep during your simulation how you want cfx to plot it? :confused:

Cirion0000 October 7, 2009 10:50

Allright, I solved that issue now I think. Now however I have a new concern, this one should be simple to solve but I can't locate how to do so. Basically I need to increase the max number of warning messages from the /NERR command but I do not know where to input it since I used ANSYS workbench to create the input file and I cannot locate the menu for it there. I can see it in the ANSYS multiphysics application but not workbench. Since I have 2000 timesteps I reach the 10,000 warning limit very quickly. (Not fatal warnings just minor warnings basically telling me that the loads are small and such.)

lingdeer November 29, 2011 13:30

Though it is a post 2 years ago, I hope somebody can give me some advice:

Here is the /NERR command:
http://www.kxcad.net/ansys/ANSYS/ans...lp_C_NERR.html

I have the same problem with no. of warning message. I m using ANSYS 13

I actually added
/uis,msgpop
/nopr
/NERR,,,-2

So that ANSYS won't prompt me for warning message
Finally I can successfully start a simulation.
But after a lot of timesteps, the no. of warning messages exceed 10000 and stopped my simulations.

I tried to change to
/NERR,,99999,-2

But seems ANSYS cannot recognize this command and aborted my run.


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