[Sigi]

Hello everyone,

I'm currently running a simulation involving a pitching airfoil at a specific frequency. In this simulation, I've applied FFT in Matlab to analyze the x and y coordinates of the airfoil's motion over multiple periods. What's interesting is that both the primary frequency of oscillation and higher harmonics of that frequency are present in both the x and y coordinates. This holds true for both the "moving the entire grid" and "mesh deformation" options.

One possible explanation I can offer is that there's an interaction occurring between points, where some are primarily influenced by the fundamental frequency, while others are influenced by higher harmonics. However, if each point were solely influenced by a single frequency, it would have been easier for me to interpret the results.

I'm wondering if the presence of these higher harmonics might be due to factors such as nonlinearity, or numerical issues. For the majority of points in the simulation, the influence of higher harmonics (e.g., 3rd harmonics and beyond) appears to be negligible. Nevertheless, I'm curious about the underlying reasons for this behavior.

I'd greatly appreciate any insights or explanations you may have regarding this unexpected behavior.

Thank you!