Steady flow

The flow of a fluid is steady if its velocity, pressure and all the numerical values relating to its substance (e.g. density and viscosity) are independent of time at every point in the flow field. A steady flow is in principle only possible in a condition of equilibrium (steady state).

A turbulent flow is, strictly speaking, a transient flow as the turbulent fluctuations are statistically irregular, time-dependent phenomena. However, a turbulent flow can be treated as a steady flow with reasonable accuracy, if the time-averaged values of velocity, pressure etc. are taken into account.

The same applies to the absolute velocity within, and in close proximity to, the impellers of centrifugal pumps, which in the strict sense is (periodically) transient due to the finite number of vanes. However, when the values averaged over time are taken into to account, it can be considered steady.