these simulation numerique et modelisation de l'ecoulement autour ...

LES of a bi-periodic turbulent flow with effusion 19
SUCTION WALL
y
z
x
Figure 12. Time-averaged solution from Run C over a cutting plane located in the suction side
at 0.5 d below the plate. The thick black/white ellipses correspond to the projection of the aperture
inlet. (a): Contours and isolines of time-averaged streamwise velocity. (b): Contours and
isolines of time-averaged normal velocity. (c): Contours and isolines of time-averaged spanwise
velocity. (d): Contours of Q criterion. Isolines of time-averaged streamwise velocity as in (a). A
schematic in the centre of the figure shows the direction of rotation of the vortices; the dotted
line shows the location of the cutting plane y = −2.5 d displayed in this figure.
This criterion, based on the second invariant of the velocity gradient tensor, is used to
locate vortical structures: when the Q criterion is positive, the rotation rate is superior
to the strain rate. In figure 12(d), positive values of the Q criterion are observed downstream
of the hole. Two counter-rotating streamwise vortices are created at the lateral
edges of the hole: their distance to the suction wall is approximately 0.5 d. A schematic
in the middle of figure 12 shows the direction of rotation of the vortices. Downstream
of the perforation, the spanwise spacing between the vortices increases and they slightly
move away from the suction wall. This vortical structure has already been reported both
experimentally and numerically in MacManus & Eaton (2000), where their formation
process is detailed. Figures 12(a,d) also show that the streamwise vortices delimitate the
low streamwise velocity zones (shown by isolines).
The flow near the perforated plate on the suction side proves to be highly threedimensional,
with streamwise vortices appearing downstream of the perforation. This
organisation is then very different from an idealised concept of a uniform suction.