Hi
Fortunately I was able to find a solution. I still consider described problem as a bug, because the workaround was to merge first two layer surfs (counting from edges – where was this problem with selecting faces). To make it more clear: then I had two surfaces which couldnt be added togather to system coupling region. Now, after merging these surfs I can add them to system coupling region and problem with mesh quality on trailing edge dissapeared because of improved mapping (was about 95%, now is 100%). Solution converges even when heavily loaded, with big displacements, of course using URF.
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