Editing Potential flow (section)

===Line source and sink===
A line source or sink of strength <math>Q</math> (<math>Q>0</math> for source and <math>Q<0</math> for sink) is given by the potential

<math display="block">w = \frac{Q}{2\pi} \ln z</math>

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

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

i.e., a purely radial flow.