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Surface roughness can be used to transition the boundary layer from a laminar to a turbulent flow. Early separation on an airfoil causes an increase in drag. You can trip the flow with surface roughness, suction/blowing, trip wire, etc to make it turbulent and repair the separation.
Now relating to the article I am guessing they have a turbulent boundary layer which is why sand particles are being sucked in and slammed against the blade. Having a laminar BL would prevent sand from entering it?