A steady flow is present if the flow velocity and the cross-sectional area of the flow (and thus also the flow ) are not subject to any change over time , i.e. if the following applies at each individual location:
- the flow velocity
- the cross-sectional area flowed through
- the time .
The flow velocity and cross-sectional area can vary between different locations. In this case, the system can be described by a speed field. In a steady flow, orbital and streamlines are the same; only then will the particles move on streamlines that remain constant over time, as if on fixed tracks.
Stationary uniform flow
Flow velocity and flow height are not subject to any local change along a streamline , but they can vary from streamline to streamline:
Stationary irregular flow
Flow velocity and flow height are subject to local changes: