ABSTRACT
Turbulence is a state in which fluid particles move chaotically. Even though the fluid equations are deterministic, turbulent motion of individual fluid particles is unpredictable due to an intrinsic instability of such a motion, i.e. great sensitivity of the fluid paths to slight disturbances. In this, turbulence is similar to a gas of molecules: even if one uses deterministic laws of classical mechanics to describe the motion and collisions of the molecules, their individual tracks are impossible to predict. However, in both the turbulence theory and the kinetic theory of gases one deals with averaged quantities which are possible to describe and predict, such as the mean concentration of molecules in gas, or a mean velocity profile distribution (in both gas and turbulence), or the mean velocity distribution of gas molecules, or a mean distribution of energy over the turbulent eddies.
