Question

Which of the following statements is true regarding one and two-dimensional flows?

(a) Flow in a pipe is always taken as one-dimensional flow

(b) Flow in a pipe is always taken as two-dimensional flow

(c) Flow in a pipe is taken as one-dimensional flow when average flow parameters are considered

(d) Flow in a pipe is taken as two-dimensional flow when average flow parameters are considered

The question was posed to me during an interview.

The doubt is from Types of Fluid Flow in section Kinematics of Flow and Ideal Flow of Fluid Mechanics

Answer 1

Right choice is (c) Flow in a pipe is taken as one-dimensional flow when average flow parameters are considered

Explanation: The flow inside a pipe can be described by the cylindrical co-ordinate system (r; θ; z), where r is in the radial direction, θ in the angular direction and z in the axial direction. For a circular cross-sections, the flow can be taken to be independent of θ. Hence, it can be taken aa a two-dimensional flow. Again if aerage flow parameters are considered to account for the variation in the radial direction, the flow can be taken as an one-dimensional flow.