Physics of Fluids,
Journal Year:
2024,
Volume and Issue:
36(2)
Published: Feb. 1, 2024
The
decelerating
swirling
flow
in
the
draft
tube
of
hydraulic
turbines
at
part
load
conditions
often
results
a
self-induced
instability
known
as
vortex
rope.
This
phenomenon
is
associated
with
detrimental
pressure
pulsations
hydropower
system
that
need
to
be
mitigated.
A
deep
understanding
such
essential
for
developing
effective
mitigation
and
control
strategies.
current
article
exploits
dynamic
mode
decomposition
(DMD)
algorithm
perform
an
in-depth
modal
analysis
physical
aspects
DMD
can
efficiently
identify
distinct
coherent
structures
isolated
frequencies.
sparsity-promoting
variant
exploited
extract
most
influential
modes.
computational
fluid
dynamics
(CFD)
data
generated
via
resolved
improved
delayed
detached
eddy
simulation
using
OpenFOAM.
Frequency
CFD
uncovered
peaks
normalized
frequencies
f/fn=0.56
0.63,
whose
origins
seemed
initially
unclear.
Nevertheless,
elucidates
these
excitations
are
rotation
reunited
fluctuations
separated
boundary
layer,
respectively.
non-linear
field
unveiled
through
revealing
distinctive
These
include
rotational
plunging
modes
rope,
traveling
wakes
blades,
layer
separation
due
strong
adverse
gradient,
core.
reconstruction
time
highlights
while
it
possible
achieve
perfect
considering
all
recovered
modes,
model
typically
fails
predict
future
behavior
acceptable
level
accuracy.
chaotic
nature
turbulent
presents
substantial
challenge
predicting
built
based
on
prior
events.
not
only
provides
more
comprehensive
physics
underlying
rope
but
also
lays
groundwork
potential
applications
controlling
mechanisms.
Physics of Fluids,
Journal Year:
2024,
Volume and Issue:
36(4)
Published: April 1, 2024
This
article
details
the
construction
of
an
experimental
visualization
platform
for
observing
cavitation.
The
uses
high-speed
photography
and
particle
image
velocimetry
(PIV)
techniques
to
conduct
research
into
flow
pattern
vortex
field
cavitation
in
Venturi
tubes.
Dynamic
mode
decomposition
is
employed
extract
energy
distribution
characteristics
field.
Cavitation
occurs
at
exit-to-inlet
pressure
ratio
0.595,
length
zone
increases
as
this
decreases.
When
reaches
0.280,
rate
remains
almost
constant
becomes
chocked.
shape
evolves
periodically
chocking
flow,
can
be
divided
three
parts:
initiation
development
area,
a
fusion
collapse
area.
area
exhibits
periodic
changes
form
contraction,
expansion,
re-contraction.
Near
wall,
complex
boundary
conditions,
with
re-entrant
jet
causing
bubble
aggregation,
rolling,
shedding.
PIV
extraction
reveal
that
vortices
primarily
appear
near
where
they
undergo
process
fragmentation
fusion.
strength
small–large–small
related
cloud
shedding
caused
by
jet.
Physics of Fluids,
Journal Year:
2021,
Volume and Issue:
33(11)
Published: Nov. 1, 2021
The
objective
of
this
paper
is
to
identify
the
dominant
coherent
structures
within
cavitating
flow
around
a
Clark-Y
hydrofoil
using
two
data-driven
modal
decomposition
methods,
proper
orthogonal
(POD)
and
dynamic
mode
(DMD).
A
snapshot
data
sequence
obtained
large
eddy
simulation
interaction
between
cavitation
vortex
during
cloud
cavity
shedding
evolution
investigated.
Modal
via
POD
DMD
indicates
that
include
large-scale
cavity–vortex,
re-entrant
jet,
shear
layer,
small-scale
in
wake.
In
addition,
field
can
be
reconstructed
from
most
energetic
or
modes.
errors
reconstructions
produced
first
four
modes,
eight
modes
are
3.884%,
3.240%,
3.889%,
respectively.
Furthermore,
transient
predicted
method
with
an
error
8.081%.
largest
results
occur
mostly
trailing
edge,
near
provide
accurate
practically
beneficial
techniques
for
understanding
flow,
although
substantial
challenges
remain
regard
predicting
intense
nonlinear
system.
