Question

What is the no-slip condition? What causes it?

Short answer

Answer: The no-slip condition is a fluid flow boundary condition which states that the fluid velocity at a solid boundary is equal to the velocity of the solid surface, meaning the fluid particles at the interface share the same speed as the solid surface. This condition arises from the interaction between fluid molecules and the solid surface, as fluid particles tend to stick to the solid due to forces like adhesive forces, Van der Waals forces, and electrostatic forces.

Step-by-step solution

Definition of No-Slip Condition

The no-slip condition is a common fluid flow boundary condition which states that, at a solid boundary, the fluid velocity is equal to the velocity of the solid surface. In other words, the fluid particles at the interface between the fluid and a solid surface have the same speed as the solid surface.

Cause of No-Slip Condition

The no-slip condition arises from the interaction between fluid molecules and the solid surface. When fluid particles are in contact with a solid surface, they tend to stick to it due to various forces, which include adhesive forces, Van der Waals forces, and electrostatic forces. As the fluid is in contact with the solid surface, the velocity of fluid particles decreases due to friction. Ultimately, fluid particles at the interface share the same velocity with the solid surface forming a layer known as the boundary layer.

Example of the No-Slip Condition

To better understand the no-slip condition, let's consider a common example: fluid flow over a flat horizontal plate. When the fluid flows over a stationary plate, the no-slip condition implies that the fluid particles in direct contact with the stationary plate will have zero velocity. As we move away from the plate, the layer of fluid with a non-zero velocity increases, thus forming a boundary layer. The formation of the boundary layer highlights the impact of the no-slip condition on the fluid flow characteristics.