# Weissenberg number

The Weissenberg number (Wi) is a dimensionless number used in the study of viscoelastic flows. It is named after Karl Weissenberg. The dimensionless number is the ratio of the relaxation time of the fluid and a specific process time. For instance, in simple steady shear, the Weissenberg number, often abbreviated as Wi or We, is defined as the shear rate $\dot{\gamma}$ times the relaxation time $\lambda$
$\text{Wi} = \dot{\gamma} \lambda.\,$