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-   -   Tascflow - Turbomachinery related (http://www.cfd-online.com/Forums/cfx/19584-tascflow-turbomachinery-related.html)

centaur_ks April 23, 2003 13:28

Tascflow - Turbomachinery related
 
Hi all

i am trying to simulate a compressor impeller using cfx-tascflow 2.12. i set everything .. but when i try to solve it during 1st time step it tells me

stop due to error : fatal overflow in liner solver

i tried to change the memory allocations and doubled the memory for tascflow3d but still its buggin me.

any suggestions what might be going wrong.

thanks in advance.


BAK_FLOW April 25, 2003 08:58

Re: Tascflow - Turbomachinery related
 
Hi,

TASCflow is a coupled solver which means that the equations for mass, u, v, w-momentum are solved simultaneously at each time step. As a result you usually need a reasonable initial guess or the solver may fail. There are a number of things you can do to get a better initial guess:

1. Solve a simpler problem ie. laminar (turbmd=f), frozen turbulence (tke_and_epsilon=f), etc

2. Generate a reasonable guess for the machine using the turbo initial guess, etc

3. Under relax the solution lots by using a smaller time step.

Given that the solver starts and then has a fatal overflow it already has enough memory so increasing the memory will have no effect.

Best of luck,

BAK_FLOW

Martin Bowers April 25, 2003 11:01

Re: Tascflow - Turbomachinery related
 
Try the turbo initial guess but don't use the machine specific settings, just the generic and set reasonable inlet and outlet p. Also starting up with etfact = 1 is a lot more robust and then switch to dtime. The high speed impinging flow at the LE present in the initial guess seems to always kill the solver if etfact isn't used, unless you want to try first order! But then you actually have to stop the solver to switch to iskew=3..


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