Anem。meter Reading in the Presence 0麦 Nearby 。bstacーe

551．508．5
Nearby Obstacle
Anemometer Reading in the Presence o圭
by
M。Sanuki
C6％惚1！晩オ6070109加106s脚α渉07ツ
S．Kimura and S．Toyama
・∼レZ6！60701092αzl R6s6‘z70h乃zs渉πz6渉6
（Received September30，1955）
Abstract
A three−cup anemometer and a combination windサane ahd ane−
mometer model are tested in wind tunnel as to their rotational speed in
the presence of a cylindrical obstacle．Somewhat￠onsistent and
remarkable errors in reading，especia11y in the lee．side，areσbserved
which shou1（1be taken into account in wind spee（1m6asurement at
tower鞠pylons etc。
1． Object
Ground−based anemometry is often effected with anemometers installe（1at the
side of towers，pylons etc．Especially，the gradient of wind speed is always
measured with this installation．The present experiment is scoped to clarify the
magnitude and correction of errors caused by this installation．
2． Methoαof experiment
The cup anemometer and the combination wind vane and anemometer model
are set respectively according to the scheme illustrate（1in Figs．1an（12，aroun（1
of the1．5−meter wind tunnel
of the Institute， the ane−
mometer being set in the
horizontal Plane passing the
mid−point of the cylinder．
The cup anemometer is
of the standar（i type hav−
ing three cups of diame−
ter100mm and cup．center
diameter of200mm． The
③
／
＠
1
4 ．7 夢
3∬
350
q 矯略
吐ゴ霧
←一％一一一乃o，→
き疇§唱も、＼Φ■§嘆
across the free air stream
も
亀
ー監暮量−−量−−ーー86，馨畦量4−−，喜−ーロ踵5昌ー−−馨8
cylinder is placed vertically
iも噂う−
and4＝100，44．7and22mm
in case of combination
anemometer mode1． The
、乗ミ
in case of cup anemometer，
ー
ー−書⋮⋮：L馨ー屡⋮⋮聾⋮1
さ§§ミ駕㌔、Φ§良
a circular cylinder of diame−
ter4＝150，100and44．7mm
Fig。L Arrangement of the cup anemometer around the
cylin（1er（Plan view，unit in mm）．
Anemometer Reading in the Presence of Nearby Obstacle
L
⑤
←卿．昇ク150＿
しド
Fig．2．Arrangement of the combination model around
the cylinder（plan view，unit in n｝m）．
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1も竜十
蝋勤
／
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、磯！
④盈
③
さも、黛蓉喚鵠Φ、㍉もミ受
⋮ーー；L
1955
141
combination anemometer is
an 1：2．5scale model of
Speedovane（an experiment−
al combination wind vane
and anemometer，also Ref．
【11）having a windmill or a
prop611er of diameter140mm
and total fuselage Iength of
272mm．
The anemometer read−
ing is first taken at the
location of the cylinder with
the cylinder removed。This
reading iS regarded aS COm−
parison base an（l other rea（1−
ings are expressed as its
：fractions。
Fo】f the combination
model the deviation of the
fuselage center line from the direction of the tumel Bow is also observed。
All observations are conducted in the steady state of the tunnel flow・
3． Exper三mental results
1）Cupanemometer
The most remarkable effect is found in the lee−side of the cylinder，as illustrated
in Fig．3，whereハワノVo stan（is for the ratio of anemometer readings with and with−
out the presence of the cylinder．The abscissa represents distance measured
windward or leeward from the cylinder center，expressed in multiple of cylinder
diameter．This shield一 ∠0
∠0
ψ臨44z＿2。
ing effeCt is sO COn−
sPicuous in the lee−
〃＝κ33
％ 44ク
side that the sole
practical remedy is to
％謡2．o
install an anmometer
withcup center dia−
meter∠）1arger than at
〃
一〇5
least丘ve times the 賜
cylinder diameter 4
〃
0．5
％
（Fig．3b）． The wind−
〆
垢諾∠35
Ward StagnatiOn effeCt
is much milder and the
anemOmeter reading at
distances larger than
・four times the cylinder
diameter will give suf−
Hcient accuracy （Fig．
3a）．
The anemometer
0
0
／04 5 0 0 5 〃4
齢η‘んvα♪4 ∠eθwα雇
‘α） 6δ♪
Fig． 3．Cup anemometer reading at various distances wind−
ward and leeward of the cylinder（4：cylinder diameter，
P：cup center diameter，M。R．L wind tunne1）．
142
M．Sanuki，S．Kimura and S．Toyama
Vo1。VI No．2
reading段t both sides of the cylinder gives only minor deviations，amounting
ノ〉／ムηoニ0．99at position3in Fig。1an（1LO2at position4，for three sizes of cylinder・
This msymmetry is caused by the direction of anemometer rotation as皿ustrated
in Fig．1，as the near flow to the cylinder is more accelerated than that at the
far side．Tぬe resulted effect has the tendency to accelerate the anemometer at
position4more than that at position30wing to the fact that the driving cup
（recessing in the wind）of the former is closer than that of the latter・The
wind tunnel free bouudary has nothing to do with this unsymmetry，as is ascer−
tained from a separate experiment．
The results in Fig．3are tested up to wind spee（10f20m／s aロd it is found
that the wind speed has very little effect on them．
2） Combination anemometer
The results are i11ustrated in Fig．4．The shielding effect is similar to the
∠0 ／0
砂初
麟
∠ンげ講6．∂6
娠竺3．13
〃
〃
一〇．5
％
毎
ゆ
4
一〇5
％
0 0
んr4 ／0 5 0 0 5 〃！ぜ 204
酩，74’豚6ひ4 ∠eθレγα！・4
似♪ ．（ゆ）
Fig．4．Combination anemometer reading at various distances windward and leeward
of the cylinder（4：cylinder diameter，D：propeller diameter，M．R．1．wind tumel）．
case of cup anemometer，an（i the propeller diameter Z）should be taken not less
than six times the cylinder diameter4，if the anemometer reading is effected in
the lee−side．In the windward side a propeller diameter larger than three times
the cylinder diameter will be satisfactory．In both cases the location of the
anemometer should probably be taken at distances larger than five to ten times
the cylinder diameter．
The deviation of the fuselage center line from the tunnel fiow（1irection is
most fierce at position6in case of cylinder diameter100mm，where．speed
measurement is h4rdly possible．Other positions give deviations of from several
degrees to10。right or left，even in case of the smallest cylinder diameter44．7mm，
except wind．ward locations．
The anemometer reading at both sides of the cylinder gives．〈ワノ〉o＝0．95for
4＝100mm，and．〈ワ．〈乙o＝1．O for4二44．7and22mm．No msymmetry is observed in
these cases．
All the tests are conducted up to wind speed of10m／s．
4． Conclusions
1） The cup center diameter of a cup anemometer should be taken larger
1955
143
Anemometer Reading in the Presence of Nearby Obstacle
than at least five times the diameter of the obstacle，in order to obtain satis．
factory reading．This is more essential than the distance of the anemometer
location which will be taken not less than four times the obstacle diameter．
2） The propeller diameter of a combination anemometer should be taken
larger than at least six times the diameter of出e obstacle．This is more import−
ant，h6re again than the insta11atioll distance，which need not exceed five to tell
times the diameter of the obstacle．
R碗76銘06
【1】
SANuKI，M・and KIMuRA，S．，1954：Experiments on a Marine Combination Wind Vane
and Anemometer in Pitching or Rolling Motion，Pap．Met．Geophys。，
3，p．35。

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