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-   -   Transient axial turbine case issues (http://www.cfd-online.com/Forums/cfx/83530-transient-axial-turbine-case-issues.html)

sherifkadry January 2, 2011 22:28

Transient axial turbine case issues
 
Hey Everyone, happy new year. I was hoping for some insight from some turbo cfx users. I have been running a simulation of a 1.5 stage axial turbine (Stator-Rotor-Stator), I'm using a total pressure inlet and massflow specification at the second stator outlet.
I've been running this model in transient mode, with a time step corresponding to a 0.008 pitch travel per step(forgot to mention that the stators and rotor stages both have a numbering of 50, and are modeled with one passage each). I've run the case to 3 pitch travels and what I see after about 1.5 pitch travels I get this sudden increase in all parameters and no temporal periodicity (this is noticed whilst monitioring some massFlow averaged locations with time). Creating a movie, I see my wakes suddenly increasing in size after 1.5 travels, and having more of a random pattern with time versus what I would expect which is some temporal periodicity. I'm thinking this is a sign of divergence, but my residuals are basically a straight line with some flucuations but all below 1e-5. What could be causing this? Should I model more than one instance on for all the stages? Could use some insight, thanks.

SAA

fkzstar January 7, 2011 00:51

Hi, Have u tried larger time steps, say 0.05 pitch level? Any difference?


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