Direct numerical simulations of three time-developing turbulent
plane wakes have
been performed. Initial conditions for the simulations were obtained using
two realizations
of a direct simulation from a turbulent boundary layer at momentum-thickness
Reynolds number 670. In addition, extra two-dimensional disturbances were
added in
two of the cases to mimic two-dimensional forcing. The wakes are allowed
to evolve
long enough to attain approximate self-similarity, although in the strongly
forced case
this self-similarity is of short duration. For all three flows, the mass-flux
Reynolds
number (equivalent to the momentum-thickness Reynolds number in spatially
developing
wakes) is 2000, which is high enough for a short k−5/3
range to be evident in the streamwise one-dimensional velocity spectra.
The spreading rate, turbulence Reynolds number, and turbulence intensities
all
increase with forcing (by nearly an order of magnitude for the strongly
forced
case), with experimental data falling between the unforced and weakly forced
cases.
The simulation results are used in conjunction with a self-similar analysis
of the
Reynolds stress equations to develop scalings that approximately collapse
the profiles
from different wakes. Factors containing the wake spreading rate are required
to
bring profiles from different wakes into agreement. Part of the difference
between
the various cases is due to the increased level of spanwise-coherent (roughly
two-dimensional) energy in the forced cases. Forcing also has a significant
impact on
flow structure, with the forced flows exhibiting more organized large-scale
structures
similar to those observed in transitional wakes.