See this article: Aerodynamic Performance Improvements Due to Porosity in Wings at Moderate Re
Was wing porosity ever tested/used for real aircraft?
The aerodynamic efficiency parameter clearly shows the positive effect of the permeability for low angles of attack. Having a permeable section on the airfoil surface will provide better aerodynamic characteristics when the angle of attack is less than 10°. This is compatible and in agreement with the observation of other researchers on the effect of the holes on the aerodynamics characteristics of the airfoil that concluded that “at a transitional phase where Re= 40,000 and the angle of attack ranged from 0 to 9°, the L/D ratio was higher compared to the same wing without holes