Civil - Mechanics Of Fluids - Boundary Layer
BOUNDARY LAYER
1. Mention the range of Reynold's number for laminar and turbulent flow in a pipe.
If the
Reynolds number is less than 2000, the flow is laminar. But if the Reynold's number is greater than 4000, the flow is
turbulent flow.
2. What does Haigen-Poiseulle equation refer
to?
The
equation refers to the value of loss of head in a pipe of length 'L'
due to viscosity in a laminar flow.
3. What
are the factors to be determined when viscous fluid flows through the circular
pipe? The factors to be determined are:
i. Velocity distribution across the section.
ii. Ratio
of maximum velocity to the average velocity. iii. Shear stress distribution.
iv. Drop of pressure for a given length
4. Define kinetic energy correction factor?
Kinetic energy factor is defined
as the ratio of the kinetic energy of the flow per sec based on actual velocity across a section to the
kinetic energy of the flow per sec based on average velocity across the same section. It is
denoted by (?).
K.
E factor (?)
= K.E per
sec based on
actual velocity /
K.E per sec
based on Average velocity
5. Define momentum correction
factor (?):
It is defined as the ratio of
momentum of the flow per sec based on actual velocity to the momentum of the flow per sec based on average
velocity across the section.
?= Momentum per
sec based on
actual velocity/Momentum Per
sec based on
average velocity
6. Define Boundary layer.
When a real
fluid flow passed a solid boundary,
fluid layer is adhered
to the solid boundary. Due to adhesion fluid undergoes
retardation thereby developing a small region in the immediate vicinity of the boundary. This
region is known as boundary layer.
7. What is mean by boundary layer
growth?
At
subsequent points downstream
of the leading
edge, the boundary
layer region increases because the retarded fluid is
further retarded. This is referred as growth of boundary layer.
8. Classification of boundary
layer.
(i) Laminar boundary layer,
(ii) Transition zone,
(iii)Turbulent boundary layer.
9. Define Laminar boundary layer.
Near the leading edge of the
surface of the plate the thickness of boundary layer is small and flow is laminar. This layer of fluid is
said to be laminar boundary layer.
The length of the plate from the
leading edge, upto which laminar boundary layer exists is called as laminar zone. In this zone the
velocity profile is parabolic.
10. Define transition zone.
After laminar zone, the laminar
boundary layer becomes unstable and the fluid motion transformed to turbulent boundary layer. This
short length over which the changes taking place
is called
as transition zone. 11. Define Turbulent boundary.
Further
downstream of transition zone, the boundary layer is turbulent and continuous
to grow in thickness. This layer of boundary is called turbulent boundary
layer.
12. Define Laminar sub Layer
In the
turbulent boundary layer zone, adjacent to the solid surface of the plate the
velocity variation is influenced by viscous effects. Due to very small
thickness, the velocity distribution is almost linear. This region is known as
laminar sub layer.
13. Define Boundary layer Thickness.
It is
defined as the distance from the solid boundary measured in y-direction to the
point, where the velocity of fluid is approximately equal to 0.99 times the
free stream velocity
(U) of the fluid. It is denoted by ?.
14.List
the various types of boundary layer thickness.
Displacement
thickness(?*), Momentum thickness(?),
Energy thickness(?**)
15. Define displacement thickness.
The
displacement thickness (?) is defined as the distance by which the
boundary should be displaced to compensate for the reduction in flow rate on
account of boundary
layer formation.
16. Define momentum thickness.
The momentum thickness (?) is defined as should be displaced to
compensate for the reduction account of boundary layer formation. the distance
by which the boundary in momentum of the flowing fluid on
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17. Define energy thickness
The energy thickness (?**) is defined as the distance by which the
boundary should be displaced to compensate for the reduction in kinetic energy
of the flowing fluid on account of boundary layer formation.