In continuum mechanics, a power-law fluid, or the Ostwald–de Waele relationship, is a type of generalized Newtonian fluid for which the shear stress, τ, is given by τ = K n {\displaystyle \tau =K\left^{n}} where: K is the flow consistency index, ∂u/∂y is the shear rate or the velocity gradient perpendicular to the plane of shear, and n is the flow behavior index. Wikipedia