  This paper proposes a simple new closure principle for turbulent shear flows.
The turbulent flow field is divided into an outer and an inner region. The
inner region is made up of a log-law region and a wall layer. The wall layer is
viewed in terms of the well known inrush-sweep-burst sequence observed since
1967. It is modelled as a transient laminar sub-boundary layer, which obeys the
Stokes solution for an impulsively started flat plate. The wall layer may also
be modelled with a steady state solution by adding a damping function to the
log-law.
  Closure is achieved by matching the unsteady and steady state solutions at
the edge of the wall layer. This procedure in effect feeds information about
the transient coherent structures back into the time-averaged solution and
determines theoretically the numerical coefficient of the logarithmic law of
the wall
  The method gives a new technique for writing accurate wall functions, valid
for all Reynolds numbers, in computer fluid dynamics (CFD) programmes.
  Keywords: Reynolds equations, modelling, closure technique, wall layer,
log-law, CFD.
