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For finding the skin- friction drag we need to only measure shear-stress at the top or bottom surface.(a) Always true(b) Always false(c) True for flat plate, which is a symmetric airfoil(d) Depends on the Reynolds numberThis question was addressed to me in an internship interview.Origin of the question is Laminar Flow topic in chapter Incompressible Flow over Airfoils of Aerodynamics

Answer»

The correct answer is (c) True for flat plate, which is a SYMMETRIC AIRFOIL

Explanation: The shear stress distribution on the airfoil is the same at the top and BOTTOM SURFACE for a flat plate. And we can just integrate the local shear stress on one side and double the RESULT to get the total skin-friction drag.



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