non-cartesian grids occur weird line in postprocessing
 

Hi, I am running CFD of wing, but result of pressure on surface shows weird lines with extraordinary low pressure

I made a wing with CAD and converted to STL, and meshed using snappyhexmesh, and mesh resulted with cartesian meshing with lines of non-square grid.

I guess these lines are made because it have to capture the curve of airfoil, but problem is that it seems like calculation goes somehow wrong on such grids and display awkwardly different colour.

I was expecting colors divided by imaginary contour, showing somewhat
pressure distribution of airfoil theoretically should be.

Is it caused by snappyhexmesh? How can it be solved?