Find the ratio of friction drag on the front half and rear half of the flat plate kept at zero incidence in a stream of uniform velocity if the boundary layer is turbulent over the whole plate.

Question

Question

This question was previously asked in

JKSSB JE CE 2021 Official Paper Shift 3 (Held on 28 Oct 2021)

Answer 1

Concept:

For the turbulent boundary layer, the average drag coefficient CD is prescribed by the relation:

Drag force for flat plate(F_D):

i.e.

Now Drag force on the front half

Drag force on the rear half

Now, the ratio of friction drag on the front half and rear half of the flat plate

= 1.347

Hence, the ratio of friction drag on the front half and rear half of the flat plate is 1.347.