a
Co esponding au ho : uho cak@ me. u b .cz
Measu emen o he ai low eloci y ups eam and downs eam a wi e
mesh using cons an empe a u e anemome y
F an isek Lizal1, Jan Tuho cak1,a and Mi osla Jicha1
1B no Uni e si y o Technology, Facul y o Mechanical Enginee ing, Ene gy Ins i u e, Technicka 2896/2 B no 616 69,
Czech Republic
Abs ac . Measu emen o eloci y ups eam and downs eam a special wi e mesh was pe o med o asce ain
he e ec o he mesh on he low. The mesh consis ed o wo componen s, a basic ec angula mesh wi h mesh
wid h 1.22 mm and wi e diame e 0.2 mm, and a op s eel wool wi h andom posi ion o wi es and wi e
diame e 0.05 mm. The eloci y was measu ed by Cons an Tempe a u e Anemome y using single wi e p obe
in a Plexiglas channel o ec angula c oss-sec ion. As a i s s ep, measu emen o one ho izon al and one
e ical measu ing line was pe o med 10 mm ups eam and 6 mm downs eam he wi e mesh. A spa ial
eloci y p o ile ups eam o he wi e mesh was smoo h, while he downs eam eloci y p o ile was highly
dis u bed. Howe e , eloci y luc ua ions exp essed in e ms o u bulence in ensi y downs eam o he wi e
mesh we e a enua ed down o 1%. Fu he measu emen s o he a ea downs eam he wi e mesh will be
pe o med o desc ibe he de elopmen o he low.
1 In oduc ion
Wi e meshes a e commonly used o modi y he low
condi ions, o en o emo e pa icles om he low o o
adjus he le el o eloci y luc ua ions. They a e applied
as pa s o deposi ion de ices [1] o as gas bu ne s [2].
The mos de ailed a en ion was howe e de o ed o wi e
meshes used o gene a ion o educ ion o u bulence in
wind unnels.
The i s s udies on he use o wi e meshes o
adjus men o low in wind unnels da es back o 1930s,
bu he esea ch con inues un il nowadays [3]. Acco ding
o Co sin [4] h ee condi ions ha e o be sa is ied o
achie e homogenous u bulen low ield in he wake o a
mesh. Fi s , he po osi y, ȕ, which is de ined as a a io o
open o o al a ea o a mesh in a plana p ojec ion, should
be la ge enough o p e en coalescing je s and la ge-scale
ins abili y downs eam o he mesh. Co sin sugges ed he
exis ence o a ce ain c i ical po osi y alue abo e which
uns able je coalescence does no occu . The alue o
c i ical po osi y was hen in es iga ed by many
esea che s and hey p oposed c i ical po osi ies alues
be ween 54 % and 63 % [5]. Second, he heigh o a low
channel should be much la ge han he leng h scale o
he ene gy-con aining eddies, which is o he same o de
as he mesh size. The mesh wid h, M, is de ined as a
dis ance be ween cen e s o wo adjacen wi es. The
second condi ion ensu es ha he e ec o walls on he
low will be minimal. Thi d, he measu emen s should be
aken a leas 40 mesh sizes downs eam o he mesh,
since only a e his dis ance he u bulence becomes
homogenous.
As ollows om p e ious discussion, he
cha ac e is ic ea u es o a mesh a e i s wid h, M,
diame e o wi e, d, and po osi y, ȕ.
(1)
Also i s coun e pa , i.e. he solidi y, ı, which is gi en
as 1− ȕ, is o en used.
Cu en s udy was pe o med on a wi e mesh wi h
mo e complica ed s uc u e han he meshes used in wind
unnels. The cu en mesh is being used o an indus ial
applica ion, whe e he low ield immedia ely
downs eam is signi ican . Da a p esen ed he e a e esul
o he i s p elimina y measu emen and will be
supplemen ed in nea u u e wi h mo e de ailed
measu emen in mul iple downs eam posi ions.
The mesh consis s o a basic ec angula mesh wi h
Mb = 1.22 mm and db = 0.2 mm and a op s eel wool wi h
andom posi ion o wi es and d = 0.05 mm. Ra io o he
olume o he pu e s eel calcula ed om weigh and he
ou e olume o he mesh is 0.1. This alue can be
conside ed as he olume po osi y. Howe e , po osi y ȕ
in plana p ojec ion is inhomogeneous due o andom
posi ion o op s eel wool wi es and can be assessed by
alues 10 % o 20 %. I means ha je s eme ging om
he mesh a e coalescing and c ea e la ge-scale
ins abili ies. Mesh Reynolds numbe can be calcula ed as
This is an Open Access a icle dis ibu ed unde he e ms o he C ea i e Commons A ibu ion License 2.0, which pe mi s un es ic ed use, dis ibu ion, and
ep oduc ion in any medium, p o ided he o iginal wo k is p ope ly ci ed.
DOI: 10.1051/
C
Owned by he au ho s, published by EDP Sciences, 2014
, 02068 (2014)
/201
67
epjcon
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A icle a ailable a h p://www.epj-con e ences.o g o h p://dx.doi.o g/10.1051/epjcon /20146702068
ReM = U.M/Ȟ, whe e U is he mean eloci y, M is he
mesh wid h and Ȟ is he kinema ic iscosi y [5]. The ac
ha a wi e mesh ei he gene a es o damps u bulence
depends on a alue o Reynolds numbe . Unde a c i ical
alue o Re = 40 iscosi y helps o damp eddies as hey
pass h ough he sc een, whe eas o e his alue o ices
a e gene a ed by he mesh [3]. In ou case mesh Reynolds
numbe ReM = 7 means ha he mesh should supp ess he
u bulence. I is wo h no ing ha he abo e men ioned
heo e ical assump ions a e alid o simple o mul i-
scale [6] g ids, howe e , hei alidi y o cu en mesh
wi h op s eel wool should be e i ied.
2 Desc ip ion o a es bench
The main pa o a es bench is a anspa en Plexiglas
channel o med om 2 sec ions. The i s , inpu sec ion,
has in e nal dimensions 1000 x 200 x 60 mm, he second,
ou pu sec ion, has in e nal dimensions 500 x 200 x
60 mm. The wi e mesh was as ened be ween he wo
sec ions and sealed by plas ic sealan Lukop en T 1990.
Fou en ance holes o CTA p obe we e d illed in o he
channel. Two on he uppe su ace, ups eam and
downs eam he wi e mesh, and wo on he side, again
ups eam and downs eam he wi e mesh app oxima ely
10 mm dis an om he mesh. The es bench was
ho izon ally aligned using wa e -le el. A scheme o he
es bench is in Figu e 1.
Figu e 1. A scheme o he es bench.
The ai low was induced by a an which was
egula ed using ol age ans o me . A educing shee
adap e was used o conduc he low om he ci cula
c oss-sec ion o he ec angula c oss-sec ion o he
channel. The angle o expansion o he adap e was 4° o
p e en low de achmen . Honeycomb low s aigh ene
was placed a he en ance c oss-sec ion o he channel o
ensu e homogenous low. Uni o mi y o he low was
e i ied using a smoke isualiza ion (Figu e 2).
The low came o he wi e mesh om he side o he
basic ec angula mesh, which co esponded o ac ual
posi ion in he eal applica ion.
Figu e 2. Smoke isualiza ion o he low ups eam he mesh.
3 Me hodology
The measu emen was pe o med by he igh angle CTA
p obe 55P04. I has pla inum-pla ed ungs en wi e wi h
diame e o 5 µm, whose o e all leng h is 3 mm, howe e
he sensi i e wi e leng h is 1.25 mm. The senso
possesses high low sensi i i y and wide equency
esponse bu ea u es conside ably low p ong- o-senso
in luence due o i s gold-pla ed wi e ends.
Calib a ion o he CTA p obe was pe o med be o e
each measu emen using s anda d Dan ec calib a ion uni
54H01. A p essu e d op on he calib a o nozzle was
measu ed using p essu e measu ing calib a ion de ice
Ai low KAL 84. Calib a ion was pe o med o
eloci ies in a ange o 0.4 m/s o 6 m/s.
Sampling equency du ing measu emen was 11 kHz
and 32768 samples we e measu ed in each measu ing
poin . Mean eloci y was hen calcula ed om all 32768
samples and u bulence in ensi y Tu = u ms/Um was
calcula ed om he oo mean squa e alue o eloci y
u ms di ided by he mean eloci y Um.
Measu emen was pe o med in ou measu ing lines
(one ho izon al line ups eam he wi e mesh, one
ho izon al line downs eam he mesh, one e ical line
ups eam and one e ical line downs eam he wi e
mesh). Posi ion o he p obe du ing measu emen o
ho izon al line ups eam he mesh is p esen ed a
Figu e 3. The sensing elemen o he p obe was 10 mm
dis an om he mesh du ing he measu emen s ups eam
he mesh and 6 mm dis an om he mesh du ing he
measu emen s downs eam he mesh.
Figu e 3. Posi ion o he p obe du ing measu emen o
ho izon al line ups eam he mesh.
Posi ioning o he wi e was pe o med using one-
dimensional manual a e sing de ice. Resolu ion o he
de ice is 0.1 mm. The o igin o he coo dina e sys em
was always se 1 mm om he side wall o he channel
using a g aph pape .
A p obe suppo holde was aligned ho izon ally o
e ically using wa e -le el. A diame e o he p obe
suppo is app oxima ely 2 mm, while he diame e o
p obe suppo holde is 4 mm. Because he seal o he
en ance hole i ed igh ly o he suppo holde , bu no
o he p obe suppo , i was necessa y o es ic a e se
ange o p e en he p obe suppo un o he hole in o de
o a oid ai leakage a ound he p obe suppo and
de o ma ion o he low ield. The e o e he ho izon al
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02068-p.2
measu ing lines co e ed 180 mm o he o al 200 mm
wid h o he channel and he e ical lines co e ed 40 mm
o he o al 60 mm o he channel heigh . The dis ance
be ween measu ing poin s in a measu ing line was 1 mm
o bo h ho izon al and e ical lines, i.e. ho izon al lines
ha e 180 measu ing poin s and e ical lines ha e 40
measu ing poin s.
The o al low a e h ough he wi e mesh was
14.16 Li e /min, which co esponds o a e age eloci y
1.18 m/s. The low a e was con olled using labo a o y
ol age ans o me which p o ided powe o he an.
4 Resul s
The measu emen o ho izon al lines ups eam he wi e
mesh was pe o med h ee imes o e alua e s a is ical
measu es o unce ain y. The second epe i ion was
pe o med in condi ions o epea abili y; he hi d
epe i ion was pe o med in condi ions o ep oducibili y
- a e a lapse o ime, a e a new calib a ion o CTA
p obe, new se up o en ila o , wi h new ope a o o he
a e sing de ice and a new posi ioning o he a e sing
de ice. No signi ican di e ences we e ound among he
measu emen s. Coe icien o a ia ion (CV) was
calcula ed om he h ee measu emen s wi h esul ing
a e age CV = 1.88 %.
Figu e 4. A compa ison o eloci y p o ile immedia ely
ups eam and downs eam he wi e mesh in a ho izon al
measu ing line.
The measu emen o ho izon al line downs eam he
wi e mesh was pe o med wice o e i y he accu acy o
posi ioning o he CTA p obe and also o e i y s abili y
o he measu ed eloci y p o ile. The eloci y p o ile
downs eam he wi e mesh was highly nonuni o m wi h
sudden changes in eloci y along he measu ed line. I is
a esul o a low condi ions c ea ed by he wi e mesh.
The measu emen e ealed se ies o high- eloci y je s
behind ou le s o mini-channels c ea ed by wi es o he
op s eel wool and wakes behind clus e s o wi es. The
wo measu emen s o eloci y p o ile ga e iden ical
esul s; a e age di e ence be ween he wo
measu emen s in measu ed poin s was 0.28 % o he
mean eloci y.
Compa ison o eloci y p o iles ups eam and
downs eam he wi e mesh is p esen ed in Figu es 4 and 5
o ho izon al and e ical lines, espec i ely.
Figu e 5. A compa ison o eloci y p o ile immedia ely
ups eam and downs eam he wi e mesh in a e ical measu ing
line.
Figu e 6. A compa ison o u bulence in ensi y p o ile
immedia ely ups eam and downs eam he wi e mesh in a
ho izon al measu ing line.
Figu e 7. A compa ison o u bulence in ensi y p o ile
immedia ely ups eam and downs eam he wi e mesh in a
e ical measu ing line.
Tu bulence in ensi ies e alua ed om measu emen s
o ho izon al and e ical lines ups eam and downs eam
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02068-p.3
he wi e mesh a e p esen ed in Figu es 6 and 7. I is
appa en ha he u bulence in ensi y dec eases
downs eam he wi e mesh as a esul o inc ease o local
mean eloci y in he je s. Fo all he abo e men ioned
cha s he abscissa ep esen s X o Z coo dina es, whe e
he coo dina e X o Z = 0 deno es he posi ion 1 mm
dis an om he channel wall. The o igin o e ical axis
is a he bo om o he channel, while he o igin o he
ho izon al line is on he le side o he channel in he
low di ec ion.
5 Discussion
The p esen ed da a a e only he p e ace o he
measu emen o he in luence o he wi e mesh wi h op
s eel wool on he low ield. The a en ion will be now
ocused on he ene gy decay downs eam he wi e mesh.
Classical heo ies o g id u bulence sugges ollowing
o mula o calcula ion o ene gy decay:
(2)
Whe e, a, is a cons an ha depends on a me hod o
u bulence gene a ion, n, is a cons an which depends on
a ype o u bulence, x0, is he loca ion o he i ual
o igin and, l0, is some cha ac e is ic leng h scale, usually
he mesh wid h. Howe e , he exp ession is alid only i
he low is homogeneous and close o iso opic. I means
ha he o mula can be used only in he a ield
downs eam he mesh.
K ogs ad [7] measu ed ene gy decay in bo h nea and
a ield using classical and mul i-scale g ids and he
sugges s ollowing exp ession:
(3)
Whe e xpeak is a dis ance whe e (u ms/Um)2 eaches i s
maximal alue. Howe e he low ield downs eam he
wi e mesh wi h op s eel wool is expec ed o be
signi ican ly di e en and hence he ene gy decay may
ollow di e en exp ession.
The ollowing measu emen will be pe o med using
X-p obe, i means wo componen s o eloci y will be
measu ed simul aneously. Also au oma ic a e sing
de ice will be used o allow o posi ioning o he p obe
in o de o measu e he ene gy decay. Howe e , as
no iced by K ogs ad [7], high a en ion should be de o ed
o ho wi e anemome y measu emen in he nea ield as
nega i e eloci ies may appea in a dis ance up o en
imes he mesh wid h om he mesh, which could lead o
signi ican measu emen e o . Lase Dopple
Anemome y can be used o compa ison, as wo
componen sys em is a ailable in he labo a o y.
Also he p essu e d op on he wi e mesh will be
measu ed, as his was iden i ied as an impo an
pa ame e o he p ac ical applica ion.
6 Summa y
A i s measu emen o wo-componen special wi e mesh
was pe o med o in es iga e he eloci y ield
immedia ely ups eam and downs eam he mesh. The
low h ough he mesh is di e en om mos cases
published in li e a u e, as mos measu emen s we e
pe o med using single laye g ids ei he wi h simple
ec angula g id o wi h mul i-scale g ids. The po osi y o
cu en g id is low and he e o e coalescing je s occu
downs eam he mesh. Cons an Tempe a u e
Anemome y measu emen e ealed highly dis u bed
eloci y p o ile downs eam he mesh, whe eas
u bulence in ensi y dec eased due o he inc ease in local
mean eloci y.
Following measu emen will be ocused on he ene gy
decay downs eam he mesh in o de o e i y
applicabili y o exp essions de i ed o single laye g ids.
Acknowledgemen
This wo k was suppo ed by he p ojec FSI-S-11-6.
F an isek Lizal was suppo ed by he p ojec
CZ.1.07/2.3.00/30.0039 o B no Uni e si y o
Technology. The au ho s acknowledge also inancial
suppo om Ope a ional P og amme “Resea ch and
De elopmen o Inno a ions” – “NETME Cen e – New
Technologies o Mechanical Enginee ing” Reg. No.
CZ.1.05/2.1.00/01.0002. The au ho s a e g a e ul o
Jakub Elcne and Milosla Belka o a echnical
assis ance.
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