In fluid dynamics, the fluid [[flow]] is often decomposed into a mean flow – and deviations from the mean. The averaging can be done either in space or in time, or by ensemble averaging.

===== Example =====

Calculation of the mean flow may often be as simple as the mathematical mean: simply add up the given flow rates and then divide the final figure by the number of initial readings.

For example, given two discharges (Q) of 3 m³/s and 5 m³/s, we can use these flow rates Q to calculate the mean flow rate Qmean. Which in this case is Qmean = 4 m³/s.