Question

If the diameter of the pipe is given as D, what is the maximum thickness of the boundary layer?

• A. 0
• B. $\frac{D}{2}$
• C. D
• D. 2D

Answer 1

The correct option is B $\frac{D}{2}$

• A pipe may be considered as a flat plate wrapped around to reform itself. Thus, fluid velocity starts at zero at the pipe wall and reaches a maximum value at the centre line of a straight pipe. It then return to zero velocity at the opposite wall of the pipe forming the velocity profile which is bullet shaped.
• $\text{As the flow enters the pipe, the boundary layer thickness will increase parabolically starting from zero to}\frac{d}{2}\text{(at centre).}$