[zacko]

Hello,

kind of hard to find a right topic for this.
I am currently trying to make a performance curve of a four-stage axial comrpessor. I have reference values of massflow rates which i need to achieve. The problem was that this setup has an average pressure at the outlet. So I needed to change the pressure and get hopefully the right massflow (kind of tricky but that should not be the focus right now).
Now I want to start new with a massflow at the outlet (like recommended in the CFX guide).
Is there a problem to use my current simulations with the ave pressure at outlet as initial value? Or does this only work when they both have the exact same BC? Cause last week when I started it quickly, there was an error. Do I need to interpolate something?

Thank you very much

[AtoHM]

Why dont just run it without initial values and with the new massflow-BC and see what happens?

What was the exact error you got? It might not even be related to the BCs.

[zacko]

Originally Posted by AtoHM

Why dont just run it without initial values and with the new massflow-BC and see what happens?

What was the exact error you got? It might not even be related to the BCs.

Yes, that would be an option, but i wanted have a better convergence maybe!:

I got several Messages like the following:
______________________________________________
Parallel run: Received message from slave
-----------------------------------------
Slave partition : 2
Slave routine : get_TWFTFC
Master location : End of Continuity Loop
Message label : 009100015
Message follows below - :
+--------------------------------------------------------------------+
| ****** Notice ****** |
| The non-dimensional near wall temperature (T+) has been clipped |
| for calculation of Wall Heat Transfer Coefficient. |
| |
| Boundary Condition : S4 Hub |
| T+ clip value = 1.0000E-10 |
| |
| If this situation persists and you are using the High Speed Model, |
| consider enabling Mach number based blending between low speed and |
| high speed wall functions. You can do so by specifying a Mach |
| number threshold as follows: |
| |
| EXPERT PARAMETERS: |
| highspeed wf mach threshold = 0.1 # default=0.0 (off) |
| END |
+--------------------------------------------------------------------+
+--------------------------------------------------------------------+
| Notice: The maximum Mach number is 4.325E+09. |
+--------------------------------------------------------------------+

================================================== ====================
OUTER LOOP ITERATION = 4 CPU SECONDS = 1.739E+03
----------------------------------------------------------------------
| Equation | Rate | RMS Res | Max Res | Linear Solution |
+----------------------+------+---------+---------+------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Floating point exception: Overflow |
| |
| |
| |
| |
| |
+--------------------------------------------------------------------+

[zacko]

I guess i found a problem.
In my previous simulations I calculated the massFlow for the whole 360° model and set it as BC. Therefore the Mach-Number is damn high.
But i needed to set only the massflow calculated for 1 passage I guess.

[Opaque]

If you are building a performance curve using ANSYS tools, I advise you to use the "Exit Corrected Mass Flow" boundary condition for the whole range.

It will converge better than splitting the curve into a pressure outlet range, and a mass flow outlet range of simulations.

The true physical mass flow is reported during the run; therefore, you can verify it is the intended mass flow for your plots.