The
aerodynamic
characteristics
of
a
square
cylinder
in
streamwise
sinusoidal
flows
with
non-zero
mean
velocity
are
investigated
numerically
by
large
eddy
simulation.
ratio
the
inflow
frequency
fu
to
natural
Karman
vortex
shedding
fvs
varies
from
0.125
8.
fluctuating
intensity
5%
20%.
forces,
pressures,
time-averaged
flow
structures,
and
dynamics
investigated.
results
show
that
effects
limited
for
cases
lower
within
(0.125fvs,
fvs)
become
pronounced
when
frequencies
(fvs,
8fvs).
As
increases
4
fvs,
recirculation
regions
on
lateral
surface
keep
shrinking
toward
leading
edge,
resulting
reattachment
shear
layer
side
surface.
strength
is
weakened
due
less
intensified
interactions
wake
region,
attains
minimum
separated–reattaching
fields.
variation
structures
deformation
pressure
distribution,
lager
negative
pressures
surfaces
recovery
leeward
wall.
drag
root
(r.m.s.)
lift
forces
decrease
during
this
process.
further
8
layers
tend
vent
again.
intensity,
force,
r.m.s.
force
increase
reversely,
maintaining
level
than
those
smooth
flow.
In
addition,
found
be
dominated
inflow-induced
gradient
field.
intensities
magnifies
flows.
This
study
proposes
a
three-dimensional
mode-based
surrogate
framework
to
predict
the
tornado-like
vortex
(TLV)
derived
from
fuzzy
neural
network
and
delayed
proper
orthogonal
decomposition
method.
First,
near-break-down
TLV
is
simulated
via
large-eddy
simulation,
its
mean,
fluctuating
statistical
flow
feature
analyzed.
Then,
spatiotemporal
features
of
coherent
structure
are
extracted
interpreted.
Next,
capability
proposed
future
state
an
unsteady
chaotic
field
systematically
evaluated,
including
variation
velocity,
pressure,
vorticities
as
well
statistics.
Finally,
parametric
analysis
also
conducted
investigate
influence
three
key
parameters
[i.e.,
Fuzzy
rules
or
output
(K1
K2),
time
embedding
number
(d)]
contained
in
step
forward
prediction
(K)
on
predicted
accuracy.
Results
show
that
for
TLV,
wandering
effect
largely
affects
dynamical
feature,
characteristics
distinct,
exhibiting
essence
swirling
jet
flow.
3D
model
can
correctly
with
relative
error
less
than
2%
radial,
tangential,
vertical
velocity
component.
It
found
time-delayed
has
great
Thus,
achieve
optimal
predicting
effect,
it
suggested
d
taken
8,
K1,
K2
18,
when
making
multi-step
predictions,
largest
K
should
not
exceed
7.
Journal of Fluid Mechanics,
Год журнала:
2023,
Номер
959
Опубликована: Март 22, 2023
This
serial
work
presents
a
Linear-Time-Invariance
(LTI)
notion
to
the
Koopman
analysis,
finding
consistent
and
physically
meaningful
modes
addressing
long-standing
problem
of
fluid-structure
interactions:
deterministically
relating
fluid
structure.
Part
1
(Li
et
al.,
2022)
developed
Koopman-LTI
architecture
applied
it
pedagogical
prism
wake.
By
systematic
procedure,
LTI
generated
sampling-independent
linearization
that
captured
all
recurring
dynamics,
six
corresponding,
orthogonal,
in-synch
excitation-structure
response
mechanisms.
2
analyzes
modal
duplets'
underpin
their
physical
interpretations,
providing
phenomenological
revelation
subcritical
dynamical
mode
shape,
results
show
two
mechanisms
at
St1=0.1242
St5=0.0497
describe
shear
layer
associated
B\'ernard-K\'arm\'an
shedding,
turbulence
production,
which
together
overwhelm
upstream
crosswind
walls
by
instigating
reattachment-type
response.
The
on-wind
walls'
similarity
renders
them
spectrally
unified
interface.
Another
four
harmonic
counterparts,
namely
subharmonic
St7=0.0683,
second
St3=0.2422,
ultra-harmonics
St7
=0.1739
St13=0.1935,
govern
downstream
wall.
2P
wake
is
also
observed
as
an
embedded
bluff-body
Finally,
this
discovered
vortex
breathing
phenomenon,
describing
constant
energy
exchange
in
wake's
circulation-entrainment-deposition
processes.
With
Koopman-LTI,
one
may
pinpoint
exact
excitations
responsible
for
specific
structural
response,
or
vice
versa.
This
study
focuses
on
the
aerodynamic
nonlinearity
and
flow
field
phenomenology
of
structure-motion-induced
dynamics
in
fluid–structure
interactions
(FSI),
which
is
essential
for
response
prediction.
Through
dynamic-meshing
large-eddy
simulations
with
near-wall
resolution,
nonlinear
damping
still
wind
has
been
isolated
by
forced
vibration,
its
phenomenological
characteristics
physical
mechanisms
have
analyzed.
The
results
show
that
can
account
up
to
30%
total
damping,
cannot
be
ignored
also
reveals
three-dimensional
vorticity
vary
nonlinearly
structure
motion,
leading
hysteresis
effect
between
forces
displacement.
Furthermore,
in-depth
analysis
discloses
eight
types
coherent
substructures,
including
Stick,
Phone,
Bowknot,
Crutch,
Droplet,
Bat,
Horn,
Flag
are
solely
induced
structural
motion.
Insights
into
these
substructures'
formation,
evolvement,
dissipation,
superposable
magnitude
disclosed.
research
offers
a
new
perspective
understanding
nature
FSI,
serving
as
reference
various
FSI
applications,
bridges,
high-building
design,
other
related
fields.
