Aerospace Research Communications,
Journal Year:
2023,
Volume and Issue:
1
Published: Dec. 18, 2023
Riblets
are
small
protruding
surfaces
along
the
direction
of
flow,
and
one
most
well-known
passive
turbulent
drag
reduction
methods.
We
investigated
a
scalloped
riblet,
shape
which
was
constructed
by
smoothly
connecting
two
third-order
polynomials
not
as
sharp
in
tip
corresponding
triangular
riblets
with
same
height-width
ratio.
Numerical
simulations
were
performed
for
channel
flow
without
riblet
control
at
an
estimated
optimum
width
W+=20
ratio
id="m2">0.5
.
A
rate
id="m3">5.77%
obtained,
is
generally
larger
than
reported
rates
from
literature.
Mean
fields
second-order
statistics
velocity,
vorticity,
Liutex,
quantity
introduced
to
represent
vortices,
reported.
It
found
that
streamwise
vortices
just
above
tips,
have
length
scale
id="m4">200−300
wall
units,
important
influence
on
those
thus
turbulence
generation
cycle
mechanism.
Pre-multiplied
energy
spectra
velocity
Liutex
component
reveal
scales
field.
Instantaneous
vortical
visualized
method
provided
emphases
tips.
should
be
noted
class
suitable
investigations
influences
curvatures
valley
future.
AIP Advances,
Journal Year:
2023,
Volume and Issue:
13(2)
Published: Feb. 1, 2023
The
Liutex
based
vortex
identification
method
is
superior
to
previous
methods
in
that
it
overcomes
the
issues
of
threshold
problem,
shear
contamination,
etc.,
with
a
clear
physical
meaning
direction
vector
represents
local
axis
rotation,
while
magnitude
equal
twice
angular
velocity
rigid-rotation
part
flow.
current
study
focuses
on
interaction
between
represented
rotation
and
residual
during
development
Λ
hairpin
boundary
layer
transition.
temporal–spatial
evolution
typical
vortical
structures
are
analyzed
Liutex–shear
decomposition
particular
attention
paid
position
strength
changes
shear.
Vortex
core
lines
extracted
investigate
mutual
interactions
inside
vortices.
It
demonstrated
for
vortex,
spanwise
rotating
motions
formed
at
head
region
can
persist
long
time
under
influence
surrounding
shear,
tail
stretches
down
near
wall
but
then
becomes
weaker
due
dissipation.
High-shear
regions
tend
be
located
top
or
below
When
legs
gets
stronger,
will
rolled
up
form
new
On
one
hand,
together
newly
consist
which,
turn,
leads
generation
second-
third-level
other
also
generates
many
smaller
streamwise
vortices
region.
results
show
very
important
Fluid Dynamics Research,
Journal Year:
2023,
Volume and Issue:
55(4), P. 045505 - 045505
Published: July 12, 2023
Abstract
Even
with
modern
measurement
techniques
and
data
from
direct
numerical
simulation
(DNS),
it
is
very
difficult
to
identify
the
individual
attached
eddies
understand
their
dynamical
behavior
due
multi-scale
nature
of
in
wall-bounded
flows,
which
puts
these
issues
at
center
current
debate.
However,
Liutex
vector
(
L
for
short),
a
rotational
field
information
on
both
rotation
axis
swirling
strength,
has
recently
been
developed
by
Prof.
Liu’s
group
as
more
accurate
clear
definition
vortex.
Combining
conventional
methods
may
provide
detailed
about
complex
flow
structures
well
insights
into
flow’s
mixing
transport
features.
We
simulated
channel
large
eddy
implementing
an
inflow
condition
based
box
turbulence.
After
validating
results
DNS
data,
we
used
isosurfaces
profiles
track
ordered
Based
observe
numerous
turbulent
phenomena
that
have
described
other
works
different
visualization
techniques.
Moreover,
shear
contamination
wall
most
severe
while
all
root-mean-square
component
variations
are
negligible.
Due
presence
background
shear,
peak
location
vorticity
fluctuation
closer
than
corresponding
fluctuation,
displacement
brought
greatest
spanwise
(z-component)
fluctuation.
According
two-point
correlation
components,
streamwise
size
does
not
vary
considerably
y+
,
however,
increases
gradually
increases.
