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the disturbances
pa
ssing through.
Th
e
re
fore, the evolu
tio
n of
the local mean
produced by
vv dU dy
enhances
uu
by
−
uv
way of
.
30
This enhancement probably accounts for
the fact that the algebraic growth of
u
is more intense than
that of
v
and
w
. Let us conclude that the physics intrinsic to
bypass (
BP
) transition engendered by a localized disturbance
is similar to that of the transition triggered by solitary single
waves (
SWs
) in many respects. However, there are certain
noteworthy
−
2
uv dU dy
differences.
The
maximum
streamwise
disturbance
and the time
when it arises vary with
u
t
max
max
and
for
SW
s, while
and
u
∝
e
t
∝
e
u
∝
log
Re
max
max
max
in BP [SCH 01]. Yet the maximum energy
associated with the disturbance
ma
E
(the peak of the energy
over time) increases less rapidly in the case of localized
disturbances with
t
∝
e
1/ 3
max
, compared to
SW
s, for which
E
∝
Re
max
.
max
E e
∝
2
5.7.5.
Transient growth and bypass transition of the
streaks
The majority of streaks in the region of the wall are
stable, as discussed in section
5.7.2,
and the number of
unstable streaks from the viewpoint of the increase of the
normal mode is greatly limited.
Schoppa and Hussein [SCH
02] propose an additional mechanism similar to bypass
transition to explain the mechanism of regeneration of the
near-wall structures. These authors assume that the
individual modes are excited by localized initial
disturbances, in accordance with the principle of bypass
transition. An analysis of the effect of excitation of the
asymmetrical
(sinuous)
modes
is
then
performed,
30 See Chapter 1 [TAR 11a, TAR 11b].
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