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Hi Nektar++ community,

 

I recently have been having issues using the stability analysis adjoint module.

 

When running direct and adjoint stability analysis I would expect similar eigenvalues to converge. This is seen in the tutorial for ‘Global Stability Analysis: Cylinder Flow’.

 

image.pngimage.png

Where the magnitude, frequency, and growth rate results are quite similar in value for the adjoint and direct Evolution Operators.

 

 

However, from my own mesh and simulation of flow past a cylinder I get a discrepancy in the modes between direct and adjoint stability.

 

Direct:

image.png


 

Adjoint:

image.png


 

My direct stability analysis simulation gives reasonable results; agreeing with the results in the Nektar++ tutorial on direct stability of a cylinder. But the adjoint stability modes are fairly different and don't yield values close to the tutorial.

 

I have attached my case files for direct and adjoint stability. I would appreciate some insight if anyone has an idea why I have this discrepancy between direct and adjoint stability results.

 

Thank you,

Matt Duran

PhD student

University of Central Florida