摘要：Natural dissimilarity or de correlation of axial velocity and temperature
fluctuations, in a tur bulent channel flow, is studied using direct numerical
simulation, DNS. Buoyancy effects were neglected, thus the temperature was
considered as a passive scalar. A uniform energy source case for the thermal
field has been used. Results for molecular Pr or Sc numbers equal to 1.0 and
0.71 are presented. More evidences of the strong correlation of axial
velocity and temperature in the wall layer are shown, like as the
similar patter of the skin friction and streamwise vorticity correlation,
with that between wall heat flux and streamwise vorticity correlation.
The importance of the most energetic events on the dissimi larity
between the axial velocity and temperature fluctuations is examined
using conditional probability. It is shown that although the most
energetic events are responsible of the strongest instantaneous dis
similarities, their contribution to the mean dissimilarity is less than a
half in the whole channel. As a complement to many previous results in the
literature analyzing fluctuations of longitudinal velocity and temperature in
frequency domain, spectral density functions is used in order to study
dissimilarity. The results presented here include new variables, as the
spectra of the fluctuations of axial velocity and temperature difference, and
the spectra of the fluctuations of the pressure field. Spectral
density functions at different distances from the wall show, that the
main cause of dissimilarity between axial velocity and
temperature fluctuations is the shift toward higher frequencies of
temperature in comparison to any velocity components, and specially to
axial velocity, in the viscous, buffer, and beginning of the
logarithmic region. However, in contrast with this situation next to the
wall, there is a general tendency to spectral convergence at the center
of the channel. Based on the spectra of the fluctuations of the
pressure field, it appears that one can conclude that such actions next to
the wall and at the center region are driven by the pressure field. It
is speculated, however, that the commented convergence at the
center region can be greater for higher Reynolds numbers than that used
in the present work.
