I am interested to the following question, and would appreciate if anyone enlightens me the answer.

Is the thickness of boundary layer over a slender body (like a cone) at small angle of attack thinner than that over a flat plate?

no! it depends from the pressure gradient

Dear Mar,

Thank for comment. The pressure gradient along the boundary layer of a slender body is of second order small quantity, in terms of ratio of diameter to length. I am more concern about the forebody, where the pressure gradient is along the flow direction and thus reduces the boundary layer thickness.

Have you ever come across any published results on the thickness of a boundary layer along forebody of a slender body?

Thanks and regards, Bill