Editing Potential flow (section)

==Analysis for three-dimensional incompressible flows==
For three-dimensional flows, complex potential cannot be obtained.

===Point source and sink===
The velocity potential of a point source or sink of strength <math>Q</math> (<math>Q>0</math> for source and <math>Q<0</math> for sink) in spherical polar coordinates is given by

<math display="block">\phi = -\frac{Q}{4\pi r}</math>

where <math>Q</math> in fact is the volume flux across a closed surface enclosing the source or sink. The velocity field in spherical polar coordinates are

<math display="block">u_r = \frac{Q}{4\pi r^2}, \quad u_\theta=0, \quad u_\phi = 0.</math>