(Book 23.5, 6)
Mixing layers:
Asuming that the layer is dominated by a balance of inviscid
instability (stronger for thinner layers) creating turbulence, and the
diffusive effects of turbulence (which thicken the layer), viscosity
would not play a big part. Then there is no obvious nondimensional
quantity that the nondimensional ratio could depend on,
giving
linear in x. For the same reason, the
velocity profile will be similar.
Jets:
2D Wakes:
For 2D wake flow, will vary with the nondimensional
parameter
. The profiles will be similar since
the shape should tend to a finite limit far downstream.
Because of the momentum integral,
remains constant
going downstream. Estimating the change in momentum
as being caused by a Reynolds shear
force
,(eg, a mixing length estimate with
,) we get that
and
decrease as
going downstream.