experimental study on the wake structure behind a ... · hideo oshikawa and toshimitsu komatsu /...
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Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
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1877-0428 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of Dept of Transportation Engineering, University of Seoul.doi: 10.1016/j.sbspro.2016.04.019
11th International Conference of The International Institute for Infrastructure Resilience and Reconstruction (I3R2)
: Complex Disasters and Disaster Risk Management
Experimental Study on the Wake Structure behind a Cylindrical Rotator with Asymmetric Protrusions in a Unidirectional Flow
Hideo Oshikawaª , Toshimitsu Komatsub
ªDepartment of Civil Engineering and Architecture, Saga University, 1 Honjo-machi, Saga 840-8502, Japan b
Department of Urban and Environmental Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Abstract Wake structures behind a cylindrical rotator with asymmetric protrusions were investigated through a laboratory experiment. Such a cylindrical rotator could prevent a flood disaster due to the accumulation of driftwood at bridges. In this study, a rotator composed of a cylinder with five quarter-cylindrical protrusions was placed in a unidirectional flow. The rotator could rotate freely under hydrodynamic forces. The results indicate that vortices shed from the rotator affected flow structures behind the rotator. The transverse distribution of the time-average longitudinal velocity of the flow with respect to the rotator was asymmetric about the longitudinal centerline. In the accelerating area with rotation of the rotator, five vortices were obviously shed from each quarter-cylindrical protrusion in each period. Where the flow and rotation were in opposite directions, vortices formation was disrupted. A longitudinal series of vortices merged downstream, ultimately becoming a single vortex. Therefore, the wake flow becomes asymmetric in an area behind the rotator where a significant torque acts. © 2015 Hideo Oshikawa. Published by Elsevier Ltd. Selection and/or peer-review under organizing committee of I3R2 2015 Keywords: Cylindrical rotator; wake; vortex; Reynolds stress; driftwood 1. Introduction
In recent years, the frequency of torrential rains resulting in slope failure, bank erosion, and other problems has been increasing. In particular, there are many cases where driftwood flowing in medium and small rivers builds up against bridges that span the river, damming the river because the span length of the bridge is too small in some cases. As a result, overflow occurs that inundates nearby houses, shore areas, and other places resulting in massive damage, even when the flow discharge does not exceed the design high-water discharge.
Research into driftwood and measures for dealing with it have therefore become a pressing issue [1]. However, although there are examples of research into the accumulation of driftwood at bridges and houses [2-7], there are few examples of investigation into specific measures for reducing the damage caused by driftwood [1]. A detachable parapet of a bridge was proposed as a countermeasure to reduce the accumulation of driftwood and refuse during flooding [8].
Against this background, we previously proposed a method for preventing the buildup of driftwood and refuse at bridges by installing a rotating cylinder called the "rotator," which is an asymmetric structure set in front of the bridge piers, and a similar method for preventing the buildup of driftwood and refuse at bridges by wrapping the bridge piers in a rotating caterpillar fitted with an asymmetric structure [9]. These methods use the massive energy of the water flow during a flood to turn the flow direction of driftwood around a bridge pier by the rotator or the caterpillar and to promote the washing out of driftwood that would otherwise build up against the bridge pier. If there is no torque around a bridge pier without the rotator or the caterpillar, driftwood and refuse are likely to balance and accumulate there. Corresponding author. Tel.: +81-952-28-8685 ; fax: +81-952-28-8699 .
E-mail address: [email protected]
© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of Dept of Transportation Engineering, University of Seoul.
162 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
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five quarter-ce been attachen, is fixed by ly in the midace disturbancrolled and rotaze without th
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163 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
Tim
laser senslaser signultrasoniccomponenfrequency
Figuinstantanemeasurem(y=0, ±2.
3. Result
3.1. Mean
Figuvelocity oexperimeforth are the meanwhere y =one direcin the arefollows thregion. Osmaller th
me-series data osor installed unal and was fc flow velocimnts of flow vy was 100 Hz,ure 3 shows teous flow vel
ment lines (x=5, ±5.0, ±7.5,
ts and Discus
n flow velocity
ure 4 shows thof the rotator
ent—except forepresented a
n flow velocity= 0, the flow vction, and the ea near the rohe main flow
On the other hahan in the y >
of the rotatingunder the rotafound to be frmeter was usevelocity were, and the measthe definitionlocity compon=7.5, 10.0, 12±10.0, ±15.0
Fig. 3. Pla
sions
y and turbulen
he distributionand cylinder
or the frequenas dimensionley distribution velocity distribflow velocity
otator (e.g., y/due to the or
and, in the y <0 region.
Fig. 2. Rotator
g phase and floator. The mear =0.84 Hz. Thd for measurin
e measured asurement dura
ns of the O-xynents (us, vs,
2.5, 15.0, 20.0cm) in the y d
ane view of the
nce structure
n across the chjust behind e
ncy spectra (Fess quantities n
for the cylindbution for the u is larger in
/D=±0.5). In tientation of th
< 0 region, sin
r (left: plane vie
ow velocity foan rotational fhe tip speed ing the flow vat a height ofation was 6 myz coordinatews). The mea
0, 30.0, 40.0 direction.
coordinate syst
hannel of the teach cylinder Figs. 6 and 8normalized byder is left–rigrotator is asy
n the positive ythe y > 0 reghe protrusionsnce the rotator
ew; right: side v
for the rotator frequency of tratio was therelocity, and thf 3.5 cm fromin at each poin
e system and asurement poscm) in the x
tem and the me
two horizontalat x/D = 1.5.
8)—the spatiay D and/or U,
ght symmetricmmetric. Thisy region than
gion, since thes, it is understr rotates in the
view)
were synchronthe rotator warefore 2 fhe horizontal dm the channent. the direction
sitions were adirection and
asurement poin
l components In the figure
l coordinates,, respectively.about the cen
s occurs becauin the negativ
e rotator rotattood that u is e direction tha
onized by usinas determinedfr (D/2+k)/U =distribution oel floor. The
ns of each of at the intersecd 11 measurem
nt
(u, v) of the mes for the resu, flow velocit. It is clear thanter line of thuse the rotatorve y region, ptes in the direlarger than in
at opposes the
ng a digital d from the =0.64. An f the three sampling
f the three ctions of 7 ment lines
mean flow ults of this ty, and so at whereas he channel r rotates in articularly ection that n the y < 0 flow, u is
164 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
Nexturbulenc
Here, u’,averagingalthough term on trotation, [19]. Howattempted
Simisymmetribecause t
We asymmetrasymmetrconfirmedturbulencmean flowflow occufrom the
Fig. 4. L
t, Fig. 5 showce, Pr, under th
v’, and w’ ag. The spatialPr of the wa
the right-handthe spatial dewever, the firsd performing c
Fig.
ilar to the meic on y = 0, wthe rotator rotaalso investigaric turbulent ric twin peak d. In this figu
ce. Furthermorw velocity beurs in the y dirvalue of v at y
Lateral distribut
ws the distribuhe same condi
21k
Pr
are the fluctul derivatives iake flow for ad side of Eq. erivative of v wst term was arcalculations, a
5. Lateral distri
ean flow velocwhile those fates in a singlated the relatiodistribution idistributions
ure, k at bothre, these pointecomes large rection accomy = 0 being alm
tions of mean f
ution across titions as for F
'' 22 vu
''' uyuvu
ating parts ofn the equatio
any cylindrica(2), in this rewas also consround one ordand the contrib
ibutions of k an
city distributiofor the rotatore direction. on between thin Fig. 5 arowith a maxim
h points becots also match tin Fig. 4. Bec
mpanying rotatmost zero for
flow velocity ju
the channel oFig. 4. In this r
'2w
'xvv
f us, vs, and won for Pr are aal two-dimensesearch considsidered becauder of magnitubution of the s
nd Pr just behind
on in Fig. 4, tr were asymm
he asymmetricound the rotatmum value atmes larger ththe points whcause of thistion and resulthe cylinder a
ust behind the ro
of the turbulenresearch, k and
ws, respectiveapproximated sional structurdering the dis
use it was thouude larger thasecond term to
d the rotator an
the distributiometric, as sho
c mean flow vtor. For botht y/D = 0.5 anhan in the surhere the absolu
left–right asylts in advectivand considerab
otator and cylin
nt flow energyd Pr are expres
)1(
)2(
ely, and the oby a differen
re is often appstortion of theught that v mian the second o Pr was smal
d cylinder (x/D
ons of k and Pwn in Fig. 5.
velocity distribPr and k of
nd a local marroundings duute value of thymmetry of the transport, wbly negative fo
nder (x/D=1.5)
y, k, and prodssed by Eqs. (
overbars reprence method. Iproximated be flow arisingight also haveterm when w
ll.
D=1.5)
Pr for the cyli. Naturally, th
bution in Fig.f the rotator aximum at y/Due to the prodhe spatial gradhe distributionwhich can be ufor the rotator.
duction of (1) and (2).
esent time In general, y the first
g from the e an effect
we actually
inder were his is also
4 and the in Fig. 5,
D = -1 are duction of
dient of the ns, a mean understood
165 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
3.2. Perio
Figuy/D = 0.5and v*, tnondimenand the pits synchr
Ther
frequencyrotator hathe rotatoalso chan
Wheas Fig. 6,of the rotfixed cylrotation trotator, re
Vert
amplitudecylinder structure
odic variation
ure 6 shows th5 near the rotathose are nonsionalized by
phase-averagedronized norma
Fig. 7. N
re are five way of 4.2 Hz, was five protrusor rotates freelnges slightly aen the peak fre it was found tator fr = 0.84linder. Howevtime-series daegardless of w
tical flow vee of fluctuatiwas sufficienaround the cy
n characteristi
he frequency sator, and Fig. 7ondimensionaly the period Td horizontal valized flow ve
Fig. 6. F
Normalized pha
aves both u* awhich is 5 timsions, the five ly depending round fr = 0.8equency of thto be 0.97 Hz Hz, the rotatver, the perioata from the lawhether this ki
Fig. 8. Fr
elocity did noon of vertica
ntly small comylinders is not
ics of the flow
spectra Fu(f), F7 shows the tilized by U,
T (=1/fr) of thevelocities wereelocity data.
requency spectr
ase-averaged ho
and v* in Fig. mes the rotatio
waves in Figon the curren4 Hz. e flow velocitz (refer to Figtional frequenodicity investiaser and its syind of vortex s
requency spectr
ot affect the al flow velocimpared with Fdiscussed fur
w
Fv(f), and Fw(fime series of tat the same
e rotation on the calculated b
tra just behind t
orizontal velocit
7, and the sponal frequency. 7 are induce
nt in this resea
ty spectra aroug. 8), and sincency of the rotaigated in thisynchronized fshedding effec
ra just behind th
horizontal wity ws was smFu(f) and Fv(f
rther.
(f) of the flow the phase-aver point with he vertical axi
by using the ro
the rotator (x/D=
ty just behind th
pectral power y (fr = 0.84 Hd by the protr
arch and is no
und the cylinde this is relativator may be a work is basflow velocity,ct exists.
he cylinder (x/D
wake structurmall since Fw(f) in Figs. 6
velocities us, raged dimensidimensionles
is. Time interpotation signal
=1.5, y/D=0.5)
he rotator (x/D=
of each compHz) of the rotarusions on the t controlled, t
der was determvely close to taffected by voed on the ph so it arises f
D=1.5, y/D=0.5)
e of the cyliw(f) around bo
and 8. There
vs, and ws at ionless flow vss time, t/T, polation was pdata from the
=1.5, y/D=0.5)
ponent dominaator in Fig. 6.e rotator. Notethe rotational
mined at the sthe rotational ortex sheddinghase relationshfrom the rotat
)
indrical strucoth the rotatoefore, the ver
x/D = 1.5, velocity u*
which is performed e laser and
ates at the Since the
that since frequency
same point frequency
g from the hip in the tion of the
cture. The or and the rtical flow
166 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
Fig. 9. Normalized phase-averaged horizontal velocity component just behind the rotator at x/D=1.5 [i): <u>/U ; ii): <v>/U ]
Fig. 10. Normalized phase-averaged horizontal velocity component behind the rotator at x/D=2.5 [i): <u>/U ; ii): <v>/U ]
Fig. 11. Normalized phase-averaged horizontal velocity component behind the rotator at x/D=8.0 [i): <u>/U ; ii): <v>/U ]
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3u/u: -0.35 -0.2 -0.05 0.1 0.25
B
t/T
y/D A
C DE
<u>/U
i)
1
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3u/u: -0.35 -0.2 -0.05 0.1 0.25
B
t/T
y/D A
C DE
<u>/U
i)
1
B
t/T
y/D A
C DE
<u>/U
i)
1
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3v/u: -0.35 -0.2 -0.05 0.1 0.25
t/T
y/D
<v>/U
b c d ea
ii)
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3v/u: -0.35 -0.2 -0.05 0.1 0.25
t/T
y/D
<v>/U
b c d ea
ii)
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3u/u: -0.25 -0.1 0.05 0.2
t/T
A B C DE
<u>/U
i)
y/D
1
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3u/u: -0.25 -0.1 0.05 0.2
t/T
A B C DE
<u>/U
i)
y/D
1
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3u/u: -0.06 -0.03 0 0.03
Y/D
y/D
t/T
<u>/U
i)
1
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3u/u: -0.06 -0.03 0 0.03
Y/D
y/D
t/T
<u>/U
i)
1
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3v/u: -0.3 -0.15 0 0.15 0.3
c dbae
t/T
y/D
<v>/U
ii)
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3v/u: -0.3 -0.15 0 0.15 0.3
c dbae
t/T
y/D
<v>/U
ii)
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3v/u: -0.1 -0.06 -0.02 0.02 0.06 0.1
y/D
t/T
<v>/U
ii)
t
y/D
0 0.2 0.4 0.6 0.8 1-3
-2
-1
0
1
2
3v/u: -0.1 -0.06 -0.02 0.02 0.06 0.1
y/D
t/T
<v>/U
ii)
167 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
For each of the x/D measurement lines, the variation in dimensionless phase-averaged velocity was extracted by subtracting the dimensionless mean values (u/U, v/U) from each of the dimensionless phase-averaged flow velocities (u*, v*). The variation is indicated by <>. The nondimensionalized results as representative measurement lines are shown in Figs. 9 to 11. The closed solid black curves in the figures represent the approximate positions and sizes of the individual vortices, and the arrows indicate the direction of vortex rotation, that is, the direction of flow. Furthermore, the dotted closed curves similarly show examples of vortices where there is a possibility of merging. Note that in each diagram, i) shows <u>/U and ii) shows <v>/U. Although these diagrams show the periodic time lapse of the flow as detected on each of the measurement lines, this corresponds to drawing a plan view of the coherent flow structures, so-called vortices, for the case where the variations detected on the measurement lines are assumed to continue as they are by advection.
In Figs. 7, 9, and 10, symbols are assigned to each of the 5 waves produced by the protrusions for convenience. Uppercase letters are assigned to the waves for <u> and lowercase letters are assigned to the waves for <v>. Then the uppercase and lowercase letters are associated such that, for example, wave A and wave a refer to the same wave, that is a vortex, generated by the same protrusion. If we look at wave B and wave b at x/D = 1.5 near the rotator in Fig. 9, wave b takes a positive peak where the variation in wave B has a phase of zero (t/T 0.27) at y/D = 0.5, which is dominated by the amplitude of the variation. If we consider the general rotation direction of vortices separated from such a cylindrical structure, we can understand that vortices exist as shown by the solid lines in Fig. 9. 3.3. Region where the rotation direction and main flow direction are the same (y > 0)
First, we describe points such as that it can be seen that the features corresponding to the same vortex are different at a glance, as can be seen in the vortices that are significantly flattened in <u> but are not quite so distorted in <v> in Figs. 9 and 10. For example, if we investigate at y/D = 0.5 and 1.0, where five cyclic variations dominate, flattened vortices occur in <u> as a result of the vortices being stretched out in the x direction because the mean flow velocity u at y/D = 1.0 far from the cylinder is faster than u at y/D = 0.5 (refer to Fig. 4). Note that although the flattened vortices in Fig. 9 i) appear to be tilted counterclockwise, the actual flattened vortices are tilted clockwise. For <v>, mean velocity shear is small since the absolute value of mean velocity is small, as can also be seen from Fig. 4, so the distortion of the vortices is small. The shape of the actual vortices is significantly flattened—as can be envisioned by considering the combination of Fig. 9 i) and ii)—and they are also deformed in the y direction, making the shape even further deformed at some point downstream, where the vortices become more like a crescent shape than a flattened ellipse.
We now discuss transformations accompanying downstream flow of the vortices by comparing Fig. 9, where x/D = 1.5, with Fig. 10, where x/D = 2.5. In Fig. 10 ii), the positive peaks of waves a and d become smaller. Therefore, waves e and a and waves c and d continue to progressively form single vortices, as indicated by the dotted lines in the figure. Furthermore, it can also be seen from Fig. 10 i) that the negative peak disappears from wave A, and the positive regions of waves E and A progressively form a single region. It was thus inferred that merging of the vortices occurred.
In Fig. 11 i) at the downstream position x/D = 8.0, a single set of positive and negative regions exists in <u>, for example, at the period of one rotation that can be seen at y/D = 1.0. This also forms the same single set of variations in <v> in Fig. 11 ii). As a result, at a position somewhat downstream, at x/D = 8.0, a single wave corresponding to the period of one rotation was formed as a result of repeated merging of vortices. That is possibly the disappearance of weak vortices.
3.4. Region where the rotation direction and main flow direction are different (y < 0)
In the region of y < 0, where the rotation opposes the main flow, five clear waves organizing vortices were not observed even in Fig. 9 near the rotator, and the amplitudes of the waves were smaller than in the y > 0 region. In other words, the vortices that occur in the region of y < 0 are weaker than the vortices in the region of y > 0. It is inferred that either merging has already begun upstream of x/D = 1.5 or clear vortices do not necessarily occur from all five the protrusions, and there may be cases where the passage of a protrusion is accompanied by only a weak perturbation not a vortex.
In the region of y < 0 slightly downstream in Fig. 10, both <u> and <v> have almost precisely a single variation in the period of one rotation. In other words, in the region of y < 0, the effect of the protrusions disappears even faster than it does in the y > 0 region. 3.5. Overall structure of mean flow and turbulence
From Figs. 9 to 11, periodic velocity variations become significant in the longitudinal vertical cross-section at y/D = 0.5 in the region of y > 0 and in the longitudinal vertical cross-section at y/D = -1.0 in the region of y < 0.
168 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
It is thereregion of
Figuphase-avethis resea
Fig.
Figu
vortices pcould alsdownstresides of yAlso in longitudincharacteri
Finabehind thshows thpointwisey = 0, andpointwiseThe pointy/D = -1significan
efore thoughtf y > 0 flow doure 12 shows teraged flow varch, <k> is ex
Fig. 12. Lo
. 13. Longitudin
ure 12 shows pass as in the so be expecteam direction.
y = 0, the vortiFig. 13, the nal measuremistics of the wally, Fig. 14 she rotator on that behind thee symmetric ad so a torque e symmetry ints where the R.0 are consistnt torque acts
t that from theownstream neathe longitudinvelocity, and Fxpressed by Eq
k
ongitudinal tran
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ed from the r In Fig. 12, aices become wmean flow v
ment range whake flow separ
shows the lonthe xy plane, e cylinder for about the origidoes not act. In the range ofReynolds stretent with the in the wake fl
e rotation of ar y/D = 0.5 an
nal transformaFig. 13 showsq. (3).
21 2u
sformation of la
ion of lateral di
twin peak disof k consistingesults in Figsalthough the rweak at the povelocity distrihere x/D 8rated from a cygitudinal tranwhich is particomparison.
in, and the forIn contrast inf x/D < 6, corss has a posititurbulent ene
low region of
the rotator, thand those in thation of the sps that of the m
22 v
ateral distributi
istributions of l
stributions thag of all freques. 9 to 11, thregion where osition x/D = 6ibution has b8.0, a velocitcylinder are mansformation oficularly repreThe Reynold
rces are nearlyFig. 14, the R
rresponding toive peak for yergy distributithe rotator.
he vortices oche region of y <anwise distribmean flow ve
2w
ions of normaliz
ongitudinal me
at have local ency componehe local maxim
the effects of6.0 since the pecome nearly
ty defect regiaintained [19].f the spanwissentative of th
ds stress arouy balanced onReynolds streso the mean floy > 0 at y/D =ion. From the
ccurring from< 0 flow down
bution of turbulocity in the m
)3(
zed <k> behind
an flow velocity
maxima at y/ents shown in ma is greatlyf the vortices eaks in <k> h
y symmetric ton remains in. e distribution he effects of tnd the cylind
n both sides ofss around the ow velocity re
= 0.5 and a nege above, it ca
m each protrusnstream near yulent energy <main flow dir
d the rotator
ty behind the ro
/D=0.5, -1.0 Fig. 5. Furthe
y attenuated toremain differ
have nearly disthere. Note thin Fig. 13, th
n of the Reynothe rotator, an
der in Fig. 15f the central arotator does nesults describgative peak fo
an be understo
sion in the y/D = -1.0. <k> on the rection. In
otator
where the ermore, as oward the rs on both sappeared. hat in the hat is, the
olds stress nd Fig. 15 5 is nearly axis where not exhibit ed earlier. or y < 0 at ood that a
169 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
4. Conclu
In thdue to flopier by in(1) Vor(2) Vor
flowFurperi
(3) Theaxisqua
In futhe resultaccumulapiers.
Fig. 14. Lo
Fig. 15. Lon
usions
his research, wow as part of nstalling a cylirtices are genertices in the rew (y>0) flow rthermore, theiod correspone effect of thes accompanyiantities are asyuture researchts of this res
ation of driftw
ongitudinal tran
ngitudinal trans
we conducted the developm
indrical rotatoerated by eachegion where thnear y/D = 0
e vortices mernding to the roe vortices exteing the rotatioymmetric in thh, it will be nesearch, and towood by using
nsformation of l
sformation of la
an experimenment of technoor. The followh of the five prhe direction o
0.5, and vorticrge as they fltational period
ends down to on of the rotahis region wheecessary to exao ultimately ug the rotator
lateral distribut
ateral distributio
ntal investigatology for prev
wing results werotrusions as a
of rotation of tces that occurlow downstred of the rotatoaround x/D =
ator, and the ere a significaamine the appunderstand anwhen taking
ions of Reynold
ons of Reynold
tion of the wakventing the acere obtained.a result of rotathe rotator is tr on the oppoeam, eventuallor. = 6.0 with the mean flow ve
ant torque actspropriate instand improve tinto account
ds stress behind
ds stress behind
ke structure occumulation o
ation of the rothe same as th
osite side (y<0ly forming a
asymmetric felocity and ch.
allation positiothe effectiventhe effects o
d the rotator
the cylinder
of a cylinder thof driftwood a
otator. he direction o0) flow near ysingle variati
forces about tharacteristic t
on of a rotatorness for preveof driftwood a
hat rotates at a bridge
f the main y/D =-1.0. ion with a
the central turbulence
r based on enting the and bridge
170 Hideo Oshikawa and Toshimitsu Komatsu / Procedia - Social and Behavioral Sciences 218 ( 2016 ) 161 – 170
Acknowledgements
The authors thank Naoki Terao and Kazuo Fujita for their help in performing the experiment. References
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