Questions on overlapping moving grids for airfoils in tandem configuration
 

My project is to simulate flow over 2 flapping airfoils in tandem configuration and based on many research papers, I have chosen to use the overset mesh/overlapping moving grids for the simulation.

However, the result came out to be rather weird, which can be seen from the picture attached. https://ibb.co/w06Ms2x

The Q-criterion seems to not be shed from the airfoil but around an "imaginary wall" and some of it are just permanently there.

I would like to ask if this is a problem with the overset settings, meshing problem, or any other things which I could have overlooked.

If so, what are the settings I should use or how I can fix the mesh.

Thank you.