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CXF aero damping analysis results interpretation

    • vytautas
      Subscriber

      Dear, Experts

      I have question regarding aero damping analysis:

      it was made modal analysis of propeller, it deformation was exported to cfx, made aero damping analysis according : https://www.singularityeng.com/singularity-engineering-blog/2019/1/8/predicting-damping;

      but results of aero damping curve show instability? (show in black color), however in example (last picture) no jump

      More time steps require

      Normalization made according example settings - work with this value?


      Thank You for help;

      Regards,

    • rfblumen
      Ansys Employee
      When we evaluate aerodynamic damping for a given operating condition, frequency and nodal diameter, we need to ensure that the simulation is converged and has reached a time-periodic condition. For a converged, time-periodic solution, it's expected that the value of aerodynamic damping will be varying within a small range over the period of oscillation. From your charts of aero damping versus accumulated time step, the damping hasn't settled down. This may due to:
      -Set up issues. I would review your set-up to make sure there are no errors.
      -Convergence issues. Make sure the model is converging at every time step and the run is becoming time-periodic. It looks like in your case you only ran it three periods (similar to the example case you mentioned). It may take several more periods to become time-periodic. You might want to look at CFX Tutorial 36 (Fourier Transformation Method for a Blade Flutter Case). Although in your case you're not using the Fourier Transform method, The other parts of the setup should be similar. In the tutorial, the model is run a sufficient number of periods such that the solution is time-periodic.
    • vytautas
      Subscriber
      Thank You for answer;
      regards;
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