The wall shear stress w for flow in a narrow annular gap between a fixed and a rotating cylinder is a function of density ,

The wall shear stress τw for flow in a narrow annular gap between a fixed and a rotating cylinder is a function of density ρ, viscosity μ, angular velocity Ω, outer radius R, and gap width Δr. Using (ρ, Ω, R) as repeating variables, rewrite this relation in dimensionless form.