# 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.
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

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.