Must periodic oscillation give periodic results?

zonexo

Hi,

I've investigating the thrust & efficiency of oscillating airfoils. They undergo periodic oscillation at a constant frequency (0.2-0.6) with a fixed maximum heave,pitch amplitude. Most of the results I obtain give a periodic thrust oscillation.

However, 1 or 2 particular configurations give an unsteady, non-periodic variation in the thrust/lift. The simulation has run for about 10 non-dimensional time. I wonder if I should continue until I can a periodic result or that this configuration 'll never give one in the 1st place? It's simply an unsteady non periodic case.

Can someone comment on this? Thanks