# Wall Shear Stress

## Definition - What does Wall Shear Stress mean?

Wall shear stress is the shear stress in the layer of fluid next to the wall of a pipe.

## Corrosionpedia explains Wall Shear Stress

In nonpulsatile flow in a straight vessel, fluid does not move at the same velocity at every point in the vessel. Instead, fluid flow is fastest at the center and slowest close to the wall. The fluid velocities assume a parabolic profile referred to as the "laminar flow" profile. This pattern of flow is the result of friction within the fluid and between the fluid and the vessel wall, and is related to the fluid viscosity. This friction creates a tangential force exerted by the flowing fluid and is referred to as the "wall shear stress". The magnitude of wall shear stress depends on how fast the fluid velocity increases when moving from the vessel wall toward the center of the vessel. This velocity gradient near the wall is called the "wall shear rate."

Wall shear stress is defined as:

Where µ = Dynamic viscosity

U= Flow velocity parallel to the wall

Y= Distance to the wall