Which of the following actions delay boundary layer separation on an aircraft wing upper surface?

(A) Boundary layer suction through porous surface skins

(B) Tangential high-momentum blowing into the boundary layer

(C) Vortex generators shedding streamwise vortices to re-energize the boundary layer

(D) Increasing adverse pressure gradient abruptly

Answer Key:

A,B,C

### Solution: Boundary layer control methods that delay separation include suction of low-momentum fluid (A), tangential blowing of high-momentum fluid (B), and vortex generators (C). D promotes premature separation. Correct: A, B, C.

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