For rotational and compressible flow, the velocity potential and steam function are given by, ϕ and ψ respectively. Which one of the following sets is correct?
1
\(\nabla^2\phi=0;\nabla^2\psi=0\)
2
\(\nabla^2\phi\ne0;\nabla^2\psi=0\)
3
\(\nabla^2\phi=0;\nabla^2\psi\ne0\)
4
\(\nabla^2\phi\ne0;\nabla^2\psi\ne0\)