Experimental and Numerical Study of Swirling ... - Solid Mechanics

Experi imental and Numerical N Stud dy of Swirling g Flow in Scaveenging
Processs
for 2-Stroke
Marin ne Diesel Engin nes
Figur re 4.52:
Normal lized Reynolds
Stresses in Polar
Coordin nates at z and 1
Re . A
Chapter 4
The Reynolds
stress normal n compponents
are high
in the coree
and near waall
regions.
On average the magnitudde
of shear strress
componennts,
at different
measuring
positions are a smaller than
normal streess
componennts.
Considerinng
the max ximum values s, for normal stresses at z11
ww uu
vv and ffor
shear stresses uw vw uv v
indicatingg
anisotropy of the floww.
Howeve er, with swirl decay downsstream
at z5, tthe
maximum values becomme
almost equal for ind dividual compponents
of booth
normal aand
shear streess
compon nents i.e. ww w uu vv v
and uw
vw uv .
The Reynolds
stresses decay with the swirl aand
distributtion
of normmal
and sheear
compon nents tends to o become commparatively
andd
gradually mmore
uniform in
the flow w domain. For r uu and vvv , the rotatioon
of the oval shape region to
an angl le with the axe es lines for doownstream
poositions
is not easy to explain.
Probably
it is the three dimennsionality
of f the flow pparameters
likke
asymme etric velocity distribution, helical vorteex
and wall effect etc. thhat
spreads the velocity variance unevvenly
and tiltts
the oval shhaped
region in
anticloc ckwise direct tion. Anotheer
possible reason may also be thhe
downstream
increase e in amplitudde
of precessiing
of vortexx
core which is
statistic cally observed at positions bbetween
the axxes
lines in the
instantaneouus
PIV sna apshots.
The distribution
of Reynolds R stresss
components in polar coorddinates
along X-
axis at z1 and Re is s given in figgure
4.52. Yann
et al. (20000)
used LDA to
A
measure e turbulent kinetic k energy y distribution in a confinedd
swirling floow
using a vortex cham mber that usedd
similar geommetry
of vorteex
chamber i. .e.
there is
a 90° bend ding when thhe
flow enteers
the cylindder
from swiirl
generat tor. For vv v and vv r r , the result obbtained
by Yaan
et al. (20000)
show qualitatively q
si imilar behavioor
to results shown in in figure 4.52 i. .e.
large va alues are obser rved in the vorrtex
core regioon
and at largee
radial distance
from th he cylinder axis.
The outlet
section th hat provides a flat-bottom cylinder headd
has the outllet
pipe with
the ratio of outlet to cylinder diammeter
as 0.5779.
The current
104
Swirling Flow in a Pipe