  A four component decomposition of the local instantaneous velocity is
proposed. It brings out more readily the terms in the Navier-Stokes equations
associated with different events and fluid structures of turbulent flows than
the classic two component decomposition of Reynolds. In particular the new
composition highlights the existence of two types of Reynolds stresses: fast
and slow. The fast Reynolds stresses can be linked to a streaming process that
describes the ejection of wall fluid in the bursting process. It also provides
a simple method for modelling the wall layer. The four components are a long
time average, a slow fluctuating component based on the difference between the
long term average and the smoothed phase velocity developed by passing coherent
structures, a fast fluctuating component which is periodic in nature and a
streaming component created by the interaction between the fast fluctuations
and the fluid viscous effects.
  Key words: Velocity components, bursting, streaming flow, smoothed phase
velocity, fast and slow Reynolds stresses, wall layer
