XAY DtTNG HINH HOC VA MO HINH LlTdl CHO MO PHONG DONG CHUYEN DONG QUA CHONG CHONG MO HINH BAY
GEOMETRY RECONSTRUCTION AND MESH GENERATION FOR SIMULATION OF FLOW THROUGH PROPELLERS FOR RC PLANE
Ngo Khdnh Hieu"'^', Dgng Quoc Bdo"', Phgm Minh Vuffng'^' '" Bo mon Ky thudt Hdng khong, Dgi hgc Bdch khoa Tp. HCM ''' Phong thi nghiim Trgng diem quoc gia Do luang vd diiu khiin so '^' Cong ty DFM-Engineering Tdm tat: Trong qud trinh tinh todn so dong luc hgc luu chdt, viic xdy dimg mo hinh luai di rai rgc hoa mien tinh todn co y nghia rdt quan trgng. Logi phdn tu luai, hinh dgng vd kich thuac cua cdc phdn tu lrong hi lu&i ti'nh todn co y nghia quyet djnh den toe do hgi tu, do chinh xdc cua ket qud. thai gian tinh todn cua bdi todn. Bdi bdo ndy di cap din phuang phdp xdy dung mo hinh 3D cua vgt the thirc te tir dir lieu tog do diem XYZ trong khong gian 3 chieu. dugc xdc dinh bdng phucmg phdp quel bien dgng khong tiip xiic vd dugc tiin hdnh xdy dung mo hinh luai, ddnh gid chdt lugng lu&i cho viic mo phong tinh todn sd dgng luc hgc liru chdt. Xdy dung mo hinh 3D chong chong mdy bay mo hinh vd tiin hdnh chia luai cho viec mo phong dong khi chuyin dgng qua chong chong mdy bay mo hinh trong truong deu, khong nen dugc vd su dung phdn mem ma nguon md.
Tir khda: CFD, OpenFoam, quel khong tiip xiic
Abstract: Mesh generation is a mandatory process phase in typical CFD and has an important impact on the efficiency and accuracy of computation. Element,cell shape and size play an important role in both convergence speed and numerical accuracy. This paper discuss the method of building 3D model from the co-ordinate data of XYZ in space by SCAN 3D. This 3D mesh model and the quality of the mesh is going to be evaluated. To illustrate this method.3D model propeller of UA V is built by method SCAN 3D and generated mesh from 3D model for simualtion flow through propeller of VA V with incompressibility, steady conditions and using OpenFoam software.
Keywords: CFD, OpenFoam. SCAN 3D
1. DatvUnde
Chong chong la thiet bi chuyen doi nang lucmg tir dpng ca nhiet, dong ca dien sang he thong lire day (nhu may bay, tau thiiy...) hoac chuyen doi cac nang luang tix thien nhien (gio, thuy trieu...) sang cac dang nang lugng khac nhu dien nang, ca nang 6k phuc vu cuoc song cua con nguoi. De co the danh gia ket qua mo phong so dpng lire hoc cua dong khi chuyen dong qua chong chong mpt each tot nhat trong dilu kien thirc nghiem hien co a trong va ngoai nuoc thi chong chong ciia cac mo hinh bay canh bang dieu khien dugc nhom tac gia lira chgn lam doi tugng mo phong so. Viec lua chon nay la chap nhan dugc bai thuc te chong chong mo hinh bay dugc thiet ke va ehl tao dua tren cac bien dang canh chuan va co buac chong chong dugc tinh toan nhu chong chong may bay thye xk. Cu thg: chong chong APC co bien dang dugc thiSt ke dua tren bien dang NACA 4412 va bien dang Clark-Y [1];
chong chong Master Airscrew dugc thiit kS 34
dua tren bien dang canh day co phan dau tron va phan duoi canh mong; con chong chong GWS thi dugc thiet ke dua tren bien dang canh mong vai phan dau canh mong [2].
Hinh I duai day la chong chong Master Airscrew E9x6, day la ehong chong diing rieng cho cac mo hinh bay dimg dong ca dien CO duong kinh 9 inches va buac hinh hgc cua chong chong la 6 inches.
Hinh 1 - Chong chdng Master Airscrew E9^ 6 TS. Micheal Selig cung cac cgng sir a Truang Dai hgc Illinois tai Urbana- Champaign da tien hanh xay dung ea sa du lieu hinh hgc [3] va du lieu thuc nghiem dac tinh cua chong chong ciia cac mo hinh may bay [2].
Tai Truang Dai hgc Bach khoa, Dai hgc Qu6c gia Tp. HCM, TS Ngo Khanh Hieu ciing cac cgng su da xay dung mo hinh thue nghiem khao sat dac tinh Iyc day cua chong chong may bay mo hinh [4] voi cac ket qua kha tin cay khi so sanh vai ket qua thuc nghiem cua Micheal Selig.
Bai viet se huong den xay dung mo hinh hinh hgc va mo hinh luai ciia chong chong mo hinh bay phuc vu cho mo hinh tinh toan so mo phong dac tinh cua chong chong.
Day la buac quan trgng anh huang toe do hgi tu cua bai toan va tinh chinh xac eiia ket qua mo phong so [5][6].
O cac phan tiep theo cua bai viet, nhom tac gia se trinh bay phuang phap xay dyng mo hinh hinh hgc cua chong chong bang phucmg phap do khong tiep xuc. Chong chong mo hinh duge chgn ap dung la chong chong Master Airscrew E9x6 (xem Hinh 1).
Tiep theo, phucmg phap xay dyng mo hinh luai cho chong chong va danh gia chat lugng mo hinh luai phuc vu cho cong tac mo phong dong khi ehuyen dgng qua chong chong bang chuang trinh ma nguon ma OpenFoam se dugc trinh bay.
2. Xay dimg mo hinh hinh hoc cua chong chong may bay md hinh
2.1. Vai net ve cong nghe Scan Laser
Hinh 2 - Mdy NexlEngine SD Laser Scanner
Cong nghe Scan laser la mgt trong nhimg ung dung cua cong nghe do khong tigp xiic. Trong qua trinh do may su dung chiim sang Laser chieu vao be mat chi tiet c4n do, chum tia sang dugc phan xa Iai tir be mat chi tigt dugc cam iing do thu Iai dua vao bg phan biln d6i ciia may do va vai sy ho trg cua may tinh va phan mem dieu khign cho ra kgt qua cua chi tigt duoi dang dam may digm [7]-
Thiet bi Scan Laser dugc chgn sii dung trong bai viet nay la thiet bi NextEngine 3D Laser Scanner (xem Hinh 2) cua hang NextEngine [8] [9].
2.2. Quy trinh quet chong chong Master Airscrew E9x6
Quy trinh quet chong chong Master Airscrew E9x6 dugc thuc hien qua nhimg buac sau:
Chuan bi mau va ga dof.
Cai dat thong so tren phan mem.
Xu ly so lieu quet dugc.
Xuat ket qua: chgn dii lieu xuat ra dang dam may diem de co the tign hanh xir ly kgt qua sau khi quet bang eac cong cu ho trg khac.
Hinh 2 the hien dir lieu dam may diem cua chong chong Master Airscrew E9x6 sau khi quet tir may quet NextEngine 3D Laser Scanner va dugc xir ly trgn Matlab. Che do quet dugc xac lap la quet dang Macro voi goc quet 45° (tucmg iing vai 8 mat quet cho toan bg chong chong), dp phan giai cho moi mat quet la 40000 digm/in^. Tap tin dii lieu dam may diem xuat ra tir may quet ciia chong chong nay c6 dinh dang XYZ vai tong cpng 410197 digm.
Hinh 2 - Dam mdy diem cua chong chdng Master Airscrew E9x 6 sau khi quel
2.3. Xu Iy k8t qua do
Sau khi co ket qua dam may diem XYZ, bang viec ap dung thuat toan tach eac diem trong dam may diem tai nhung vj tri mat cat xac dinh, tap hgp nhimg digm thu dugc se cho phep the hien dae tinh eua chong chong khao sat tai vi tri cat. Cac digm dugc tach dua theo vi tri ban kinh xet vai dieu kien la khoang each tu diem do dgn vi tri tam cua chong chong quet eo sai so so voi ban kinh xet bang sai so cho phep ciia thiet bi (vi du trong trucmg hgp quet a che do Macro thi sai so se la ±0.127 mm). Sau do, timg tap hgp 35
diem thu se dugc trai phang de tim bien dang cua chong chong, cung nhu goc dat va cac thong s6 hinh hpc ciia chong chong (nhu dp cong bien dang, bg day cua bien dang...) ung voi timg vi tri ban kinh xel.
Va theo do, chong chong Master Airscrew E9>:6 dugc chia thanh 40 mat cat theo vi tri ban kinh tir vj tri 0.05R dgn vi tri 0.95R (voi R la ban kinh cua chong chong quet, lrong truong hgp nay R c6 gia tri la 4.5 inch).
Hinh 3 thg hien dac tinh bign dang ciia chong chong Master Airscrew E9x6 tai vi tri 0.75R CO dugc sau khi xu Iy dir lieu dam may digm quet eiia no. Ket qua thu dugc cua bien dang chong chong khao sat tai vi tri 0.75R cho: chigu dai cung canh (co 75R) la 17.17 mm (^ 0.15R); bg day cyc dai la 2.18 mm (^
O.I27CO.75R); dp cong cue dai la 1.48 mm (~
0.086CO75R) dat dugc tai vi tri 6.87 mm (a 0.40CO75R): va goc dat la 16.94".
Hmh 3 - Bien dgng chong chdng Master Airscrew E9^ 6 tgi Vl tri 0 75R sau khi .xir ly ddm mdy diem quel
Dfii ehieu vai kgt qua khao sat ciia Dai hgc Illinois cho chong chong Master Airscrew £9^6 tai \ i tri 0.75R [3] cho thay ehjgu dai cung canh la 0.15R va goc dat la
17.79" thi sai so ciia chigu dai cung va goc dat ghi nhan tir may NextEngine 3D Laser Scanner ian lugt la 1.3% va 4.8%.
Sai so sau khi xir ly dii lieu dam may diem cua chong chong khao sat tren toan bp ban kinh quet ghi nhan dugc la duoi 2% doi vdi chigu dai cung, va dudi 5% doi vdi goc dat. Vdi bien dang dac thu ciia chong chong Master Airscrew E9>=6 noi rieng, cung nhu cua chong chong mo hinh bay noi chung thi sai so trgn la co the chap nhan dugc.
Hinh 4 thg hien mo hinh ba chigu cua chong chong Master Airscrew E9x6 d dang phan bo cua cac tap diem quet eua chong chong nay tai cac vi tri ban kinh.
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Hinh 4- Md hinh ba chiiu ciia chong chdng Master .4irscrew vdi lap hgp cdc diem quel lheo bdn kinh
2.4. Xay dwng mo hinh hinh hoc ciia chong ehong Master Airscrew E9x6
Tren co sd cac kgt qua phan ttch du- lieu dam may digm ciia chong chong quet dupc trinh bay d muc trudc, tga do cac digm quet trong mgt mat cat chong chdng se dugc xudt sang moi trudng ciia phan mem 3D SolidWork dg lign hanh xay dung mo hinh hinh hgc cua chong chong quet. Theo do, nhd vao cac cong cu ho trg ciia moi trudng SolidWord, cac mat dt se ldn lugt dugc lam tron bign dang va be mat trudc khi tign hanh dung mo hinh hinh hgc ba chieu ciia chong chong (xem Hinh 5).
Hinh 5 -Md hinh hinh hqc cua chong chdng Master Airscrew E9^ 6 dung tit ddm mdy diem quet
3 . Chia lirdi m6 hinh 3D chong chong
3.1. Xay dung md hinh lu*^
Nhu da neu phan trgn, xay dyng mo hinh ludi tinh toan cho mo phong so giu vai lro quan trgng anh hudng den toe do hpi tu va kgt qua tinh toan [5][10].
Mo hinh ludi bai bao nay dg cap phuc vu khao sat dac tinh khi dgng luc hpc cua chong ehong may bay m o hinh va hau luu cua chong chdng nay trong trudng dong khi dgu, dong CO nhdt va khong nen dugc.
Mo hinh lucji se sii dung la phdn tii ludi lam giac de rdi rac tren bg mat la canh chong chong va phSn tOr ludi tu dien dg rdi rac hoa mign tinh loan. Ph4n tu ludi tu dien giup ehdt lugng ludi 161 hon d6i vdi cac diem co hinh
hgc phiic tap. Theo danh gia so bg ban diu, vdi mo hinh ludi tren cdn khoang 2 trieu digm luai dg co kha nang eho kgt qua tdt.
Nhom tac gia chgn solver MRFSimpleFoam lrong chuang trinh OpenFoam de md phong ddng khi chuygn ddng qua chong ehong. Theo ygu cau ciia solver, mign ludi tinh loan dugc chia thanh hai viing nhu Hinh 6: viing ludi rotor quay xung quanh chong chdng va vimg ludi tinh bao quanh ben ngoai khong quay bao bgc viing ludi rotor. Be mat ludi chong chdng dupc chia bang phan tir lam giac co kich thudc tir 0.3 mm dgn 0.7 mm.
Tai digm miit canh, phan tir ludi cd kich thudc nhd hon tir O.I mm den 0.3 mm de CO the dam bao dii sd diem ludi tinh toan cho cac hien tugng vat ly xay ra lai day trong qua trinh md phdng sd nhu hien tugng tach rdi ldp bign, trudng xoay hinh thanh sau chong chong..., va khdng lam sai lech hinh dang hinh hgc ban dau ciia chong chong khao sat.
gian no kich thudc giiia cac phan tir ludi gan nhau la 1.2 [6]. Sd phan tu trong Idp bien la 322 098 phan tir, sd ldp bign 10 Idp, chieu day Idp bign dau tign 0.3 mm.
Hinh 6 - Vung Itf&i mo phdng chong chdng
Mign ludi tinh toan dugc xac djnh co kich thudc 4R trudc chong chdng, va lOR sau chong chdng va hinh lru cd ban kinh 8R bao bpc xung quanh chong chdng.
Ben canh dd, dg kgt qua tinh tot thi mo hinh ludi phai xac djnh dugc digm tach rdi ciia dong khi chuygn ddng qua bg mat chong chdng. Khoang each tir digm ludi dau tign ldi bg mat la canh chong chdng phu thudc vao md hinh roi lua chgn tinh toan va nam trong khoang y^ tir 20 den 200 [I0][6].
Tir cac thdng sd ddu vao dua ra d trdn, cd thg udc lugng y^ = I d vi tri y - 5.94x10"^
m va digm ludi dau tien dugc chgn dg xay dungmd hinh ludi cdy^=20 [11][12]. Ti sd
Hmh 7 - Mo hinh lu&i chia tren chong chong Master Airscrew E9^ 6
Hinh 7 cho lhay cac phan tir ludi dugc chia day tai cac digm hinh hgc phirc tap nhu mui canh va be mat chong chdng de cd the bat dupc diem tach rdi Idp bien tren be mat.
Tdng sd phan tu trong md hinh ludi trgn la 1320 663.
3.2. Danh gia chat Ingng Indi chia Chat lugng ludi dugc danh gia thdng qua mat do ludi, li sd knewness, ti sd thg tich giua cac phan tu gan nhau, ludi tai ldp bien de cd kha nang bat dupc cac diem tach rdi ldp bien.
Trong mo hinh ludi trgn, Idp bien dugc chia tren be mat chong chong. Mat dp ludi ldn tai cac digm hinh hpc phiic tap nhu miii canh dg cd thg cd ket qua lot lai cac khu vuc tren. Ti sd max skewness ciia md hinh ludi la 0.85, ti Ie the tich Idn nhat giiia cac phan tu (max aspect ratio) la 11.6902, day la gia trj chap nhan duge cua mpt he ludi tinh toan md phdng sd[6][i0][13].
Md hinh ludi trgn dugc sir dung de md phdng ddng khi chuygn ddng qua chong ehdng trong trudng hgp tTnh (iing vdi van tdc ddng vao chong chong la 0 m/s) vdi van ldc vdng quay ciia chong chdng 2000 RPM. Sau 3500 lan lap sai sd ciia cac gia tri van tdc Ux la I.25e-06, Uj, la 1.6e-06, U^ la 4.ie-07, ap suat la 7.74e-8. Cac sai sd tren Hinh 8 hau nhu khdng thay doi nhidu sau 3500 Ian lap chung td bai toan dang cho kdt qua hdi tu.
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Hinh 8 - Kel qud hdi lu cua mien linh sau 3500 Idn lap cua chong chdng Master Airscrew E9^ 6 lrong
diiu kien linh lai 2000 RPM 4. Ket luan
Bai bao da dua ra dugc each ap dung nguyen ly phuong phap do khdng tigp xiic cac vat the ba chieu vao khao sat hinh hgc cua chong chdng md hinh bay phuc vu cho cdng tac sao chep mau tir thuc te, cung nhu xay dyng md hinh hinh hpc cho bai loan md phdng sd dac linh ddng Iyc hpc cua chong chdng. Quy trinh xir ly sd lieu tir dam may diem XYZ dg xay dyng md hinh hinh hgc ba chigu thyc te ciia chong chong Master Airscrew E9x6 cd thg xem nhu mpt bai vi du mau cho phuong thirc xii ly ma nhdm tac gia dua ra. Viee xay dyng chuang trinh xu ly dam may diem bang cac doan code MATLAB ciing la mdt digm dang ghi nhan VI nd cho phep md rdng chuang trinh cho cac img dung hinh hpc phirc tap hem.
Ngoai ra bai viet da dua ra dugc phucmg phap xay dyng md hinh ludi va danh gia chat lugng cua mo hinh ludi de phuc vu cho cdng tac md phdng sd dac tinh khi ddng lyc hgc. Nhiing lhdng sd danh gia chal lugng ludi dugc dg cap trong bai bao nay co y nghia quan trpng giiip cong viec tinh loan khdng tdn thdi gian nhigu cho cdng viec hieu chinh ludi va dam bao kgt qua tinh toan chinh xac. Tuy nhien viee tinh toan md phdng sd cdn phu thudc vao nhieu ygu td dieu kien bien, giai thuat va muc dich can md phdng ma kdt qua khac nhau. Day la hudng phat trien tiep lheo cua nhdm tac gia, va se dugc trinh bay trong cac bai \ let sau.
Ldi cam on
Cdng trinh dupc thyc hien tai Phdng thi nghiem trpng didm Qudc gia Digu khign sd va Ky Thuat He thdng, Trudng Dai Hoc Bach Khoa, DHQG-HCM, thdng qua dg tai 38
nghign cuu cdp DHQG loai C nam 2013 (ma s6:C2013-20-03).
Tai lieu tham khao
[1] http://www. aocprop. com/v/Engineering/
engineering design.htmltfairfoil [2] John B Brandt, Michael S. Selig,
"Propeller Performance Data at Low Reynolds Numbers" 4 9 * AIAA Aerospace Sciences Meeting, 4-7 January 2011, Orlando, FL.
[3] http://www.ae.illinois.edu/m-selig/props/
propDB.hlml
[4] Ngd Khanh Hidu, Pham Qudc Hun§,
"Khdo sdt thuc nghiem dgc tinh luc day cua chong chong mdy bay mo hinh".
Tap chi Khoa hpc Cdng nghe Giao thdng van tai, Dai hpc Giao thdng van tai Tp.
HCM, Sd 5-6, 2013.
[5] Dnyanesh A. Digraskar, '^Simulations of flow over wind turbines, "M.A. thesis.
University of Massachusetts Amherst, USA, 2010.
[6] hltp://www.cfd-
online.com/Wiki/Best practice guidelin es for turbomachinerv CFD [7] Nguygn The Long, Truong Hdng Quang
Cong nghe SCAN 3D vd irng dung Dai hpc Giao thdng van tai, 2010.
[8] www.nextengine.com/
[9] Tai lieu may Next-engine 3D Scanner [10] John D. Anderson "Computational Fluid
Dynamics — The basic with applications', McGraw Hill Science/Engineering/Malh (1995).
r 111 http://www.cfd.online.com/Tools/yplus.
php
[I2]John D. Anderson Jr., "'Fundamentalof Aerodynamics", McGraw-Hill, 3^** ed., 2001.
[13] Nguyen Anh T h i , "Tinh todn so dong luc hgc luu chdt", Nha Xuat Ban Dai hgc Qudc gia TPHCM, 2011.
Ng^y nh^n bai: 08/10 nam 2013 Ng^y chdp nhSn dang: 24/10/2013 Phan bi§n: PGS. TS. Nguyen Thi?n Tong
