Hello, thank you for yor reply. 

Yes, of course I had a look to the rest of the flow field: the stagnation point on the duct is where it should be, the blade is correctly rotating, the wake is shedding downstream the rotor and its diverging, as it should. The simulation is all fine, the integral parameters are within the typical range of the application. 

Therefore, my only problem is that, if I zoom in at the duct stagnation point, the pressure contours have this local irregolarities (first figure from the top) instead of a nice levels distribution (see for instance the third picture from the top).