Question

Can the flow inside a nozzle be steady and uniform?

(a) yes

(b) never

(c) it can be steady but never uniform

(d) it can be uniform but never steady

This question was addressed to me at a job interview.

This interesting question is from Types of Fluid Flow in section Kinematics of Flow and Ideal Flow of Fluid Mechanics

Answer 1

Right choice is (c) it can be steady but never uniform

To explain: According to the continuity equation, ρAV =constant, where ρ= density, A= cross-sectional area of flow, V = velocity of flow. For a nozzle, the area gradually decreases towards it’s exit. Thus, no matter what the rate of flow is, the velocity of flow at the nozzle exit will always be greater than that at it’s entrance. Hence, it’ll always be an unsteady flow. It can be a steady flow if and only if the water level is maintained at a constant level by supplying water at the same rate as it gets discharged, else the water level will keep decreasing with time leading to an unsteady flow.