A solid surface without holes has lower friction factor.  The flow of fluid is over the surface.  The flow over a perforated body is through the holes.  This induces higher surface area and consequently higher drag when compared to flow without holes.The characteristic dimension for flow through holes is that of the diameter of the hole. The diameter of the hole will be smaller than the surface without holes.  Hence higher pressure loss or drag.

Dear Rais,

This is not an easy question to answer, especially because the Reynolds number and the shape of the body are unknown. However, I and my co-workers have done some theoretical and numerical work on the aerodynamics effects of porous materials. Our results are limited to transitional and turbulent channel flows bounded by homogeneous porous walls. In the cases we have investigated, drag increases because the presence of the porous material favors transition to turbulence or increases turbulence. Full details about the physical mechanisms behind drag increases could be found in the attached articles.

Best wishes,

Prof. Luca Cortelezzi

Department of Aerospace Science and Technology

Politecnico di Milano

Article Linear stability analysis of pressure-driven flows in channe...

Article Stability of Boundary Layers over Porous Walls with Suction

Article Direct numerical simulation of turbulent channel flow over p...

thank you so much Prof Luca Cortelezzi and K. V Sharma.Really helpful. I understand now

Professor Luca Cortelezzi...may i use this journals as my additional references for my thesis?

Thank you so much Mr Vitalii Pertsevyi