摘要：The direct numerical simulation of a fully developed turbulent flow with heat
transfer and the direct numerical simulation of a perturbed turbulent channel
flow with heat transfer, has been performed. Buoyancy effects were neglected,
thus the temperature was considered as a passive scalar. For the first
calculation, for non-perturbed flow, the isoflux, constant temperature, and
uniform energy source boundary conditions has been used for the thermal
field. Mean and turbulence values of velocity and temperature fields are
compared with data from the literature for the isoflux case. The second
calculation for the perturbed channel flow simulation with heat transfer, has
been performed to investigate velocity and temperature fields dissimilarity.
For this second calculation the uniform energy source case for the thermal
field was used. Perturbations were applied into the flow locally by blowing from
a span-wise slot at the lower wall, and suction from a similar slot at the
upper wall. In this first work on perturbed turbulent channel flow, no
developing calculation was used, rather than very small values of the
transpiration velocity and slot width has been used in conjunction with a
long periodic computational domain. The main results from this study show
that the skin-friction and the Stanton number suffer clear changes owing to
local blowing or suction. While local blowing yields a decreases of the
skin-friction and the Stanton number, local suction increases these
coefficients. Qualitatively the effects on both coefficients are similar for
every perturbation. The local extremes, however, for the skin-friction are
smaller than those for St. And also the region of velocity field affected by
the perturbation is larger than for the temperature field. The budgets for
the axial mean velocity and for the mean temperature show that the main
source of dissimilarity for blowing is the mean pressure gradient and the
convection terms. Mean pressure gradient make mean velocity to change in the
wall region in a slight smoother way than mean temperature. This small
differences in the variation of mean velocity and temperature yields
dissimilarities in the turbulence production in the budget of the second
moment of the fluctuations of axial velocity and temperature. The perturbed
mean flow transfers energy to turbulence spreading out its effect into
a larger region than those affected in the thermal field. The responsible for
these differences in the mean flow and mean thermal field is the non-local
effect of the mean pressure gradient on convection terms of the mean momentum
equation. For the fluctuations of axial velocity and temperature fields the
main causes of dissimilarity are the small differences in the behavior of the
gradient of the mean values, which yields dissimilarity mainly in the
turbulence production term.
