Question

For a streamlined body to achieve low drag coefficient, the boundary layer must_________

(a) Flow over the body

(b) Be attached to the body

(c) Move away from the body

(d) Move parallel to the body

The question was asked by my college director while I was bunking the class.

This key question is from Drag on a Sphere in portion Boundary Layer Flow & Forces on Sub-merged Bodies of Fluid Mechanics

Answer 1

Correct choice is (b) Be attached to the body

For explanation I would say: For a streamlined body to achieve low drag coefficient, the boundary layer must be attached to the surface of the body for a long time as possible. This causes the wake to be narrow.