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.
Journal of Fluids Engineering,
Journal Year:
2019,
Volume and Issue:
142(5)
Published: Dec. 9, 2019
Abstract
Cavitation
is
a
complicated
phenomenon
in
the
centrifugal
pump.
In
this
work,
improved
unsteady
calculation
model
based
on
bubble-rotation-based
Zwart–Gerber–Belamri
(BRZGB)
cavitation
used
to
investigate
cavitation-vortex-pressure
fluctuation
interaction
pump
under
partial
load
with
experimental
validation.
Spatial–temporal
evolution
of
can
be
classified
into
three
stages:
developing
stage,
shedding
and
collapsing
stage.
The
period
found
as
1/4T
(T
impeller
rotation
period),
corresponding
frequency
4fi
(fi
frequency).
On
analysis
relative
vorticity
transport
equation,
it
revealed
that
cavity
stretched
by
vortex
stretching
term
(RVS)
developed
dilation
(RVD),
they
have
great
influence
shedding.
peak
value
pressure
intensity
occurs
near
vapor–liquid
interface
at
rear,
shifts
downstream
development.
hysteresis
between
vapor
volume
fraction,
vorticity,
observed,
variation
fraction
source
interaction.
Physics of Fluids,
Journal Year:
2023,
Volume and Issue:
35(7)
Published: July 1, 2023
Sheet/cloud
cavitation
usually
leads
to
a
wide
range
of
length
scales
in
both
turbulence
and
phase
distribution
from
microbubbles
cavity
advection.
In
the
present
work,
Eulerian–Lagrangian
multiscale
model
with
two-way
coupling
is
utilized
simulate
cavitating
flow
around
(National
Advisory
Committee
for
Aeronautics)
NACA66
hydrofoil
at
an
incidence
angle
8°
number
σ
=
1.4.
The
can
simultaneously
capture
large-scale
cavities
microscale
bubbles.
features
are
good
agreement
experimental
observations
containing
not
only
periodical
formation,
growth,
detachment,
advection
cavities,
but
also
thousands
cavities.
results
show
that
overall
evolution
frequency
about
45
Hz.
Meanwhile,
dynamic
mode
decomposition
method
identify
coherent
spatial
temporal
sheet/cloud
flow,
which
indicates
complex
vortices
various
dominate
corresponding
scale,
vapor
structure
decreases
increasing
scale
Under
effect
turbulence,
break
into
microbubbles,
causing
size
discrete
bubbles
increase
rapidly
re-entrant
jet
cloud
shedding
regions.
Additionally,
bubble-size
spectrum
time-averaged
period
has
two
regimes.
For
larger
bubbles,
bubble
density
proportional
radius
power
−10/3.
smaller
exhibits
−4/3
power-law
scaling.
Physics of Fluids,
Journal Year:
2024,
Volume and Issue:
36(3)
Published: March 1, 2024
Cavitation-induced
vortex
and
energy
loss
are
critical
topics
in
the
field
of
hydraulic
machinery.
Through
a
combination
experimental
numerical
analysis,
this
paper
investigates
how
blade
loading
affects
vortical
structures
during
cavitation
waterjet
pump.
The
flow
rate
conditions
changed
tip
pressure
loading,
which
significantly
affected
trajectories
primary
leakage
secondary
cavitation.
A
considerable
gradient
at
attached
cavity
closure
region
leads
to
wall
reentrant
jet
side-entrant
jet,
resulting
an
under
developing
stage
severe
stage.
development
shedding
cavities.
Furthermore,
difference
alters
distribution
gives
rise
perpendicular
(PLV).
PLV
entrains
cavities
forms
vortex.
These
complex
induced
by
inevitably
enhance
enstrophy
lead
entropy
production
terms
viscous
dissipation,
turbulent
effect
react
differently
As
stages
developed
became
more
severe,
(S3)
decreased.
While
dissipative
S2
due
mixing
losses
occurring
increased
sharply,
dominates
total
S
results
increase
S.
