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Compared with a laminar boundary layer at the same Reynolds number, a turbulent one has

  • A.Higher skin friction and less resistance to separation
  • B.Identical skin friction and separation behaviour
  • C.Higher skin friction but greater resistance to separation
  • D.Lower skin friction and greater resistance to separation

Answer: C

Turbulent mixing brings high-momentum fluid down towards the wall, which steepens the velocity gradient there and so raises the shear stress, but that same momentum lets the layer push further into an adverse gradient before separating. Nearly every practical drag decision is a trade between these two effects.

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