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

14 S. Mendez and F. Nicoud
1.0
a
1.0
b
0.5
0.5
Cuu
0.0
Cuu
0.0
-0.5
-0.5
-1.0
-1.0
0.0
0.2
0.4
0.6
0.8
Streamwise distance
1.0
0.0
0.2
0.4
0.6
0.8
Streamwise distance
1.0
MEAN
FLOW
0
0
I
II
1
1
1.0
c
1.0
d
0.5
0.5
Cvv
0.0
Cvv
0.0
-0.5
-0.5
-1.0
-1.0
0.0
0.2
0.4
0.6
0.8
1.0
Streamwise distance
Streamwise distance
Figure 8. Streamwise autocorrelation coefficients for the streamwise [plots (a)&(b)] and normal
[plots (c)&(d)] velocity components from the 1-hole ( , Run B) and the 4-hole ( ,
Run D) computations at 1.2 diameter above the liner for paths I [plots (a)&(c)] and II [plots
(b)&(d)]. The sketch in between the plots depicts the paths along which the correlations have
been computed.
0.0
0.2
0.4
0.6
0.8
1.0
to a lack of statistical convergence. From a physical point of view, figure 8 also suggests
that the micro-jets have a strong effect on the turbulence structure. Turbulent integral
length scales L uu and L vv can be assessed by integrating C uu and C vv from 0 (reference
point) to 0.5 (half the hole-to-hole streamwise distance): this leads to L uu = 0.7 d and
L vv = 0.35 d for line I and L uu = 1.1 d and L vv = 0.7 d for line II. Two conclusions can
be drawn from these assessments: (a) the turbulent integral length scales L uu and L vv
are always of order d and not of order of the hole-to-hole distance, (b) the turbulent integral
length scales are significantly (30–50%) smaller along lines crossing the micro-jets
and larger otherwise. Although not displayed, spanwise autocorrelation coefficients have
been calculated too. No major difference between the 1-hole and 4-hole results could
be observed, the agreement being actually better than for the streamwise two-points
correlations presented in figure 8.
Single-hole computations with periodic boundary conditions allow to account for the
effect of the jets contained in the neighborhood of the jet considered: it is known that jet
interaction can considerably modify the jets behaviour (see for example Yu, Ali & Lee
2006). However, long-distance interactions, such as acoustic interactions (as in Staffelbach,
Gicquel & Poinsot (2006), with flames exciting each other in a periodic simulations
of a gas turbine combustion chamber) cannot be reproduced. In the present paper, such
type of collective interactions has not been observed in the 4-hole computation, supporting
the idea that the 1-hole computation performed with the finest grid (Run C) indeed
contains all the physics relevant to the turbulent flow over the infinite perforated plate
considered. Note however that this conclusion cannot be true for all the geometries. Figure
8(b) shows for example that if the hole streamwise spacing was twice smaller, C uu
would clearly be controlled by periodicity. It is difficult to state for which conditions