An inviscid steady incompressible flow is formed by combining a uniform flow with velocity $U_{\infty}$ and a clockwise vortex of strength $K$ at the origin, as shown in the figure. Velocity potential $(\phi)$ for the combined flow in polar coordinate $(r, \theta)$ is
- $\phi=\frac{K \theta}{2 \pi}-U_{\infty} r \cos \theta$
- $\phi=\frac{K \theta}{2 \pi}-U_{\infty} r \sin \theta$
- $\phi=K \ln r+U_{\infty} r \cos \theta$
- $\phi=-K \ln r+U_{\infty} r \sin \theta$
