In spherical polar coordinates, as in Fig. P4.12, the flow is called axisymmetric if 0 and /

In spherical polar coordinates, as in Fig. P4.12, the flow is called axisymmetric if υθ ≡ 0 and ∂ /∂φ ≡ 0, so that υr = υr(r, θ) and υθ = υθ (r, θ). Show that a stream function ψ(r, θ) exists for this case and is given by
This is called the Stokes stream function [5, p. 204].