Waves and turbulence

Observations on fluid flows indicate quite clearly that it may be feasible to distinguish between various classes of fluid motions with reasonably well-defined properties.

Before we try to investigate the feasibility of distinguishing waves from turbulence, it is important to notice that these two types of fluid motion are not the only ones. If all realizable flow patterns are assumed to be solutions to the same set of equations, then in principle they all possess the same degrees of freedom or possible modes of motion. The spatial and temporal boundary conditions appropriate for a given flow field determine which modes can and will be excited.