Stokes stream function
（重定向自Stokes streamfunction）
![Streamlines around a sphere in axisymmetric Stokes flow. At terminal velocity the drag force Fd balances the force Fg propelling the object.](/Images/godic/202502/13/Stokes_sphere.svg3949.png")
![A point plotted with cylindrical coordinates.](/Images/godic/202502/13/Cylindrical_with_grid.svg3949.png")
![A point plotted using the spherical coordinate system](/Images/godic/202502/13/Spherical_with_grid.svg3949.png")
In fluid dynamics, the Stokes stream function is used to describe the streamlines and flow velocity in a three-dimensional incompressible flow with axisymmetry. A surface with a constant value of the Stokes stream function encloses a streamtube, everywhere tangential to the flow velocity vectors. Further, the volume flux within this streamtube is constant, and all the streamlines of the flow are located on this surface. The velocity field associated with the Stokes stream function is solenoidal—it has zero divergence. This stream function is named in honor of George Gabriel Stokes.