# Transient axial rotor/stator convergence issue?

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March 16, 2010, 12:12
Transient axial rotor/stator convergence issue?
#1
New Member

Nicola Viscanti
Join Date: Apr 2009
Posts: 6
Rep Power: 10
Hi all!

I made a transient analysis of an axial rotor/stator. First of all I made a steady analysis with frozen rotor interface and I reached a good convergence after 250 iterations (between 10^-5 and 10^-6 RMS).
Then I launched the transient analysis using the steady results like initial values.
I have the same rotor/stator blades number so I used 1:1 and I have a pitch ratio that's exactly 1.
I set the total time = (2pi/rotor blades)/omega where omega is rotational speed in rad/s and I used 50 time steps.
I made 2 analysis:
1) max coeff. loop =10 (default)
2) max coeff. loop =30

B.C. are:
Inlet -> Total pressure and Total temperature, turbulence intensity 5%
Outlet-> Average static pressure
k-epsilon

I enclose 2 plots:
1) massflow goes through the stage
2) axial force on rotor blade

I expected a constant massflow. What are oscillationts in the last time steps? Did my transient analysis reach convergence?
I expected a periodic behaviour for axial force (the same value or very similar at 250 and 300 timestep) because I have pitch ratio exactly 1. I'm right? Plots are the same using max coeff. loop 10 or 30

Please any suggest is welcome!

Thank you very much!
Attached Images
 Massflow.jpg (51.8 KB, 48 views) Axial_force.jpg (62.5 KB, 38 views)

 March 16, 2010, 13:41 #2 New Member   Join Date: Apr 2009 Posts: 14 Rep Power: 10 Your calculation probably hasn't been stabilized. It takes several cycles to develop a repeated pattern. By the way, specifying pressure at both inlet and outlet is not a robust setup.