Question

When the velocity at the wall is zero, it refers to

• A. Slip condition
• B. No slip condition
• C. Adverse pressure gradient
• D. Favourable pressure gradient

Hint:

No-slip condition is fundamental in viscous fluid flow near solid boundaries.

Answer 1

The Correct Option is B

In fluid dynamics, particularly in the study of boundary layers, the behavior of fluid flow near a solid surface is characterized by the velocity of the fluid at the boundary. When the velocity of the fluid at the wall is zero, it indicates a specific condition known as the "No slip condition."

The no slip condition is a fundamental assumption in fluid mechanics where a fluid in contact with a solid boundary has zero relative velocity to the boundary. This implies that the fluid sticks to the boundary, leading to zero flow velocity at the wall, regardless of the velocity of the fluid away from the boundary.

This contrasts with the "Slip condition", where the fluid is allowed some finite velocity at the boundary, and is typically one that doesn't occur in real-world, viscous flows.
In technical terms:

For a fluid at a wall: u_wall = 0

Condition	Description
No slip condition	Velocity at the wall is zero, the fluid sticks to the boundary.
Slip condition	The fluid has a non-zero velocity at the boundary.

Thus, when the velocity at the wall is zero, it correctly refers to the No slip condition.