Measurement of the airflow velocity upstream and downstream a wire mesh using constant temperature anemometry

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 EPJ Web o Con e ences 46702068 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 EPJ Web o Con e ences 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 EFM 2013 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. Re e ences 1 Y. S. Mayya, R. Mish a, R. P aji h, B. K. Sap a, and H. S. Kushwaha, Science o he To al En i onmen 409 (2), 378 (2010). 2 O. B. Ramadan, J. E. D. Gau hie , P. M. Hughes, and R. B andon, Jou nal o Enginee ing o Gas Tu bines and Powe -T ansac ions o he Asme 131 (6) (2009). 3 T. Ku ian and J. H. M. F ansson, Fluid Dynamics Resea ch 41 (2) (2009). 4 S. Co sin, Tu bulence: Expe imen al Me hods. (Sp inge , 1963). 5 O. E unc, N. Oezyilmaz, H. Lienha , F. Du s , and K. Be ono , Jou nal o Fluid Mechanics 654, 473 (2010). 6 P. A. K ogs ad and P. A. Da idson, Jou nal o Fluid Mechanics 680, 417 (2011). 7 P.-A. K ogs ad, In e na ional Jou nal o Hea and Fluid Flow 35, 102 (2012). EPJ Web o Con e ences 02068-p.4