Wandreibungsstress
Wandreibungsstress, often referred to in English as wall shear stress (WSS), is the tangential force per unit area that a moving fluid exerts on a boundary. For Newtonian fluids, the magnitude of the wall shear stress at the wall is tau_w = mu (du/dy) evaluated at the wall, where mu is the dynamic viscosity and du/dy is the velocity gradient perpendicular to the wall. The concept generalizes to non-Newtonian fluids through the appropriate constitutive relation. Wall shear stress depends on viscosity, flow rate, the geometry of the conduit, and surface roughness, and can vary along the boundary in non-uniform flows.
In engineering, WSS is a key parameter in pipe and channel design; for laminar fully developed flow
In physiology and biology, WSS in arteries and microvessels influences endothelial cell behavior and vascular remodeling.
Wandreibungsstress is used in various fields and is related to the broader concept of shear stress.