Civil - Mechanics Of Fluids - 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
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
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.