This document discusses boundary layer theory. It introduces boundary layers, which form along surfaces where a fluid is flowing. In the boundary layer region near the surface, viscosity causes the fluid velocity to gradually increase from zero at the surface to the free stream velocity. Boundary layers can be laminar or turbulent depending on the Reynolds number. Separation occurs when the boundary layer detaches from the surface, such as in adverse pressure gradients. Methods to control separation include streamlining objects, adding roughness to promote turbulence, and accelerating the fluid within the boundary layer.

1. Boundary Layer Theory
Dr. Saurabh Sangal
Assistant Professor
Mechanical Engineering
SRMS CET, Bareilly

2. Content
• Introductiont of flow
• Boundary layer theory
• Development of Boundary over flat plate
• Boundary layer Separation
• Methods to control seperation

3. Introduction
 A fluid deforms continuously under the influence of a shear stress, no matter how
small.
 Fluid flow has all kinds of aspects:
Steady or unsteady, uniform or non-uniform, compressible or incompressible,
viscous or non-viscous, laminar or turbulent and rotational or irrotational.

4. Boundary layer
 The concept of boundary layer was first introduced by L. Prandtl in 1904 and since it
has been applied to several fluid flow problems.
 A fluid flowing over a stationary surface comes to a complete stop at the surface because
of the no-slip condition.
 In the immediate vicinity of the boundary surface, the velocity of the fluid increases
gradually from zero to the velocity of the mainstream. This region is known as boundary
layer and distance is known as boundary layer thickness.
 The flow region adjacent to the wall in which the viscous effects (and thus the velocity
gradients) are significant.

5. Development of B.L. over flat plate
 Schematic diagram of boundary layer development (Black Board).
Laminar Boundary layer
Turbulent boundary layer
 A reasonable assessment of whether the boundary layer will be laminar or
turbulent can be made by calculating the Reynold number (Re) of the local flow
conditions.

6. Boundary layer Separation
 Separation is the detachment of a boundary layer from a surface into a wake
region.
 Separation occurs in flow that is slowing down, with pressure increasing, after
passing through a diverging passage.
 The boundary layer separates in an adverse pressure gradient that the speed of
the boundary layer relative to the surface has stopped and reversed direction.
 Flow through converging and diverging section of circla cylinder (Black board)
 Laminar and turbulent boundary layer separation layer (Black board)

7. Methods of Controlling separation
 Streamlined body
 Make the flow turbulent (Roughness)
 Acceleration of the fluid in bounary layer

8. Thank You...