Engineering Questions with Answers - Multiple Choice Questions
MCQs on Hydrodynamic Boundary Layer
The concept of the hydrodynamic boundary layer was first suggested by
a) Isaac Newton
b) Ludwig Prandtl
Explanation: It was suggested by Ludwig Prandtl in 1904. This is the thin layer where velocity changes continuously.
The free stream undisturbed flow has a uniform velocity U INFINITY in the
d) Any direction
Explanation: It is in the x-direction only. Particles of fluid adhere to the plate surface as they approach it and the fluid is slowed down considerably.
he thin layer where velocity changes continuously is called
a) Differential layer
b) Thermal boundary layer
c) Hydrodynamic boundary layer
d) Velocity distribution layer
Explanation: In this layer the flow is rotational and shear stresses are present.
The conditions for flow beyond the boundary layer and its outer edge are
a) d u/d y = 0 and u = U 0
b) d u/d y = Infinity and u = U INFINITY
c) d u/d y = 1 and u = U 0
d) d u/d y = 0 and u = U INFINITY
Explanation: All the variation in fluid velocity is concentrated in a comparatively thin layer in immediate vicinity of the plate surface.
The pattern of flow in the boundary layer is judged by the
a) Reynolds number
b) Fourier number
c) Peclet number
d) Grashof number
Explanation: Re = U INFINITY x/v.
Consider the diagram given below and identify the correct option
a) The velocity gradient is zero everywhere
b) The velocity profile changes at every instant of time
c) Boundary layers from the pipe walls meet the pipe anywhere
d) Thickness of the boundary layer is limited to the pipe radius
Explanation: Thickness of the boundary layer is limited to the pipe radius because of the flow being within a confined passage.
The transition from laminar to turbulent pattern of flow occurs at values of Reynolds number between
Explanation: It occurs at a higher value. The pattern of flow in the boundary layer is judged by the Reynolds number, Re = U INFINITYY x/v.
The entrance length required for the flow to become fully-developed turbulent flow is dependent on
(i) Surface finish
(ii) Downstream conditions
(iii) Fluid properties
Identify the correct answer
a) ii and iii
b) i and iii
c) i, ii and iii
d) i and ii
Explanation: It depends on surface finishing, various upstream and downstream conditions and various fluid properties.
What is the value of the thickness of the boundary layer at leading edge of the plate?
Explanation: The thickness of the boundary layer is variable along the flow direction.
The boundary layer thickness is taken to be at a distance from the plate surface to a point at which the velocity is given by
a) u = 0.99 U INFINITY
b) u = 0.75 U INFINITY
c) u = 0.50 U INFINITY
d) u = 0.33 U INFINITY
Explanation: Velocity is one per cent of the asymptotic limit.