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A NUMERICAL SIMULATION OF THE CAVITATING FLOW IN AXIAL-FLOW WATER JET PUMP
H i Truofng Sang, Truffng Viet Anh Vien Co khi Dpng lire, Trudng Dai hpc Bach Khoa Ha Ndi
TOM T A T
Bdi bdo trinh bdy nghien cuu, mo phong dae tinh thuy dpng luc hpc cua dong chdy trong he luai cdnh cua ong phun hu&ng true trin mo hinh trdi phdng mgt cdt tru 2D. Cdc mo hinh tinh todn dong roi k-epsinol. mo hinh da pha vd xam thuc cua phdn mem AnsysFluent duac su dung. Truang dp sudt, vgn tdc cua dong chdy qua ong phun duac mo phong, dae biet la su tuang tdc cdnh cong tdc, cdnh hirang doi v&i dong chdy. Viec du bdo xdm thuc trong bam duac xet su dnh huang ciia so vong quay den hien tupmg xdm thuc tren cdnh bam vd cdnh huang dong. Kit qud mo phong gdp phdn ldm ro dqc diem xdm thuc trong thiet bi ddy kieu ong phun vd img dung trong thiit ke.
Tir khoa: Ansys Fluent; Bam hu&ng tn^c; bam tra; Xdm thuc trong bam; Mo hinh da pha.
ABSTRACT
This study presents the results of numerical simulation of hydrodynamic characteristics for 2D flattened-cylindrical flow passing an impeller and guide vanes in the axial-flow water jet pump (AxWJP). The model calculates k-epsinol turbulence, multi-phase and cavitation models of commercial software AnsysFluent are employed. The distribution of pressure, velocity of flow filed were simulated, especially the interaction between impeller blade with guide vanes are clarifyed.
The prediction of cavitation phenomena in pump was considered under the effects of the rotational speed. The simulation results contributed to the understanding inflow characteristics of Ax WJP and applicability in design improvement.
Keywords: Ansys Fluent; Axial; jet pump; Cavitation in pump; multiphasemodel.
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I.GIOI THIEU
Thidt bi day dang hudng hoic cd ket can tuong tu vdi dang bam hudng true vdi cau tao khac biet la ldi ra cd hpng phun dang cdn de tao ddng tia phan lire day tau. Ong hiit cua thiet bi thudng nam trong sudn tau de giam sue can.
Khac biet trong tinh toan thiet ke bom hudng true tuyen thdng la thiet ke thiet hi day kieu dng phun (water jet pumps - WJP) can phai tinh den cac thdng sd nhu luc day can thiet cua thiet bi day, lire can cua tau, he sd re nudc cua thiet hi,...
[I]. Vdi dae diem van hanh trong dai tdc dp rdng, nen viec nghien cuu chat lugng thuy lire cua thiet bi dng phun ludn duac quan tam nghien cuu tren thd gidi [2],[3],[4]. Trong hien dai hda trong cdng nghiep tau thuy, thidt hi dky kidu dng phun la ky thuat tien tien rat can duac phat tridn nhung chua dupc quan tam nghien cuu trong nudc. So vdi chan vit truyen thdng, thigt bi d4y dang dng phun cd uu diem la kha nang xoay trd cao, cd hieu suat, chat lupng che xam thuc va tudi thp tdt hon, tiSng dn th4p [2],[5].
Trong nghien cuu nay, sau khi thik kk man dng phun lam thiet bi day cho tau cdng suat nhd dudi 25 HP tai Trudng Dai hpc Bach Khoa Ha Ndi. Bai bao trinh bay ket qua nghien cuu, md phdng dae tinh thiiy ddng luc hpc, du bao xam thyc dua tren tinh toan md hmh 2D sau khi trai phang mat tru tiet dien canh banh cdng tac va canh hudng ddng. Viec du bao xam thuc trong bam dupc phan tich dudi su anh hudng cua ap suat, sd vdng quay
2, PHirONG PHAP VA MO HINH TINH TOAN
cinh huiVng canh c'lng trie bitr luiln hoiin
2.1. Thiet laip mo hinh
Hinh I. Md hinh trdi phdng tie mat tru sang lu&i cdnh 2D vd chia lu&i
Thiet bi day dugc thiet ke bang phuong phap Vdzcmhexenski-Pekin [6], cd thdng s6 lam viec: Luu lupng Q=0,153 (mVs); Cpt ap H-5,16 (mUp), sd vdng quay n=1.500 (v/ph).
Profil trung tara can md phdng cd thdng s6:
D=0,616(m); L=0,6 (m); V^-15,38(m/s); S6 canh cdng tac Z^_=4; canh huong Z =9. Dung mpt mat cat tru tai profil trung binh cat day canh hudng va day canh cdng sau dd trai cac day canh ra de nhan dugc 2 day canh cdng tac va hudng 2 chieu, vdi day canh cdng tac chuydn ddng theo phuong vudng gdc vdi ddng vao vdi van tdc V^^.
Khi sd vdng quay bam thay ddi, V^^ ciing thay ddi theo cac chd dp tucmg ung. Thidt lap dik kien bien tukn hoan dd md phdng ddng 2D qua 2 tang canh nay.
Viec chia ludi thuc hien theo nguyen t3c dp min nhd nhit xu4t phat tir mep canh thl hien d cudi hinh I. Vung 2 ludi cdnh uu tien mat dp ludi cao ldi vao va ldi ra. Cac thdng sd chia ludi nhu sau: Tdng sd niit ludi la 82.955; Sd phk ttr tinh toan la 39.644, kich thudc ludi trung binh 1,44, chi sd dp lech ldn nhit cua mit ludi (skewness max) la 0,88.
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2.2. Cac phirong trinh
Md hinh k-e cho ddng chay rdi dugc lua chpn de tinh toan trong nghien cuu nay bdi tinh tdng quat, dan gian va dugc ap dung kha phd bien, tin cay trong nghien cihi may canh din.
Day la md hinh ban thuc nghiem dua tren cac phuang trinh chuyen ddng rdi vdi nang lugng dpng hpc rdi k va ty le khuech tan e, sii dung hai gia thiet la ddng chay rdi hoan toan va bd qua anh hudng cua dp nhdt phan tu. Cac phuang trinh ca ban la phuang trinh lien tuc, phuang trinh Navier-Stoke va phuang trinh nang luang
m.
De md phdng viing bpt xam thuc, su dung cac he phuang trinh ddng 2 pha hoi - ldng va md hinh xam thuc trong tinh toan. Cac phuang trinh hdn hgp chat long gdm:
Phuang trinh cho phan tram the tich hoi nudc (water vapor).
6(apJ ^ . -. p D, Da dt " p Dt Phuang trinh the hien ty le thay ddi pha:
- Md hinh rdi k-e realizable, multiphase- mixture, khdng trao ddi nhiet.
- Che dp xam thuc: Ap suat hoi bao hda P^^-0,035 atm, mat dp bot khi n^ =W\
- Dieu kien md phdng: Md hinh chuyen ddng MRF, khdi canh cdng tac chuyen ddng tinh tien theo van tdc quay V^^, cac khdi khac diing yen.
Thdi gian 1 budc chuyen dpng canh (Time step): le"* s.
Dieu kien bien khdng trugt dugc ap dimg tren canh cdng tac va canh hudng. Bien tuan hoan (periodic) ap dung cho 2 phia. Dp chinh xac pha hai l e ^ pha ldng le"^.
De xac dinh trang thai xam thuc, ta dinh nghia sd xam thuc Thomas nhu sau:
_?xef-Pbh pV^ref
Trong dd: a la ty le phan tram pha hai, p - Khdi lugng rieng hdn hpp p = (1 - a)p, + ap^
RB ban kinh bpt khi [7].
2.3. Dieu kifn bien I
- Vat lieu: Nudcp,-998,2(kg/m^); Hoi
nudc -0,5542(kg/m^); • - Tham sd bien dau vac va ra dang ap H
suit (P outlet, P inlet);
- Thuat giai: Tinh toan tir ap suat, phu thudc thdi gian;
Trong dd: P^^[.va V ^^la ap suat va vSn tdc tham chieu, P^^^ la ap suat bao hda. O day, chgn P.f-P,n'P.. = 0.035atm,V^,= V,.
3. KET QuA VA THAO LUAN 3.1. Dae tinh phan bo trudng dong chay
(a) Phan bd dp sudt (atm)
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(b) Phdn bd van tdc(m/s)
• • -ij ' I 1
van tdc quay 1.500\' ph tuang duang van tdc tmh tien V^^=15.39m's. Ket qua md phdng phan bd trudng ap sual, van tdc va pha hoi- nudc nhu d hinh 1. Ta cd mdt sd nhan xet nhu sau:
Trucmg ap suat cho thay co \aing ap suat thap nhat xap xi gia tri ap suat hoi bao hoa xuat hien tai mep vao canh banh cdng tac. Vung tao ap lyc day tap trung d nua cudi bung canh
^ n g tac.
^f - Trudng van tdc cho thay phan bd van
^ c xiing canh banh cdng tac kha ddng deu nhung phan bd van tdc \Ting canh hudng cd su chenh lech ldn giira bung (trong dai 0 - 2 m/s) va lung canh hudng (trong dai 11 - 13 m/s), phan bung canh hudng cd su chen ddng chiem 10 - 20*^0 chieu rdng mang dan (\'ung van tdc 0 m/s) ga\ can tra luu lugng cung nhu su bat ddng deu trong phan bo \"an tdc a ldi ra.
- Quan sat theo dudng ddng cho thay co xoay tai bung canh hudng. vi tri ma van tdc thap dudi 2 m/s theo phan bd van tdc. Vi tri di chuyen tuong ddi cua canh banh cdng tac tac dpng den nhung xoay nay.
- Theo phan bd pha. nhan thay cd pha hai xuat hien tai mep vao canh cdng tac bao hieu trang thai ngudng bat dau xuat hien xam thuc.
3.2. Anh huoTig cua so vdng quay len hien t u g n g xam thyc
De danh gia dae tinh xam thuc \ a thuy ddng cua he ludi canh khi thiet bi day van hanh d cac tdc dp khac. ta xet sy anh hudng ciia so vdng quay trong dai tang dkn tu 1.500 v ph den 3.000v/ph Ket qua phan bd pha hoi xam thuc d) Pha hai d hinh 3. Trong dai n - 1500 - 2000 V/ph. wng Hinh 2. Phdn bd tru&ng ddng chdy vd pha hai trong xSm thuc a mep \ ao bung canh cdng tac phat
h^ thdng lu&i cdnh trien theo hudng chi^u dai bpt xam thuc loang rdng them ve phia ha luu. phia luna canh khdne Vdi dieu kien tinh toan P ^ , , r l , 0 ( a t m ) , cd xam thuc.
(c) Duong ddng
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a= 0.18; n=2.500 v/ph (y=2,\66m/s) <y=O.U: n=3.000 v/ph (v=30,76m/s) Hinh 3. Anh hu&ng sd vdng quay t&i viing xdm thuc
Vdi n = 2.500v/ph, bpt xam thuc d bung 4. KET LUAN canh keo dai ra, chiem 30% chieu dai canh, ddng
thdi xam thuc xuat hien tren ca lung canh tu diem giiia lung canh (diem ddng tach thanh) keo dai den cudi la canh. Vung canh hudng cung cd dau hieu bat dau xuat hien xam thuc d cudi lung canh.
Vdi n=3.000v/ph thi xuat hien vung bgt khi xam thuc d bung canh phat trien chiem 50%
chi6u dai cdnh, dong thdi d lung canh cdng tac xam thyc phat trien kha manh, chiem den 80%
phan chieu dai lung canh. Liic nay, xam thyc tren canh hudng xuat hen kha ro net tai nua cudi lung canh va d mep vao canh cilng bat dau xuat hi?n bgt xam thuc.
Bai bao trinh bay nghien cihi, md phdng dae tinh thiiy ddng lyc hpc cua ddng chay trong he ludi canh ciia dng phun hudng true tren md hinh trai phang mat cat try 2D bang vide su dung cac md hinh tinh toan ddng rdi k-epsinol, md hinh da pha va xam thuc ciia phkn mem AnsysFluent, ket qua chi ra mdt sd ket luan nhu sau:
- Trudng ap sudt, van tdc cua ddng chay qua dng phun cd sy tuomg tac dang ke giGa canh cdng tac va ludi canh hudng ddng gay ra phan bd xoay va chen ddng d canh hudng.
- Viec md phdng dua ra dy bao xam thyc trong ludi canh vdi sy anh hudng ldn ciia sd vdng quay, hien tugng xam thuc xuat hien theo"^"
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tuin ty: Tu mep vao bung canh sang lung canh banh cdng tac, sau dd la vung lung canh huang ddng.
- Thidt bi d i y b i t d i u cd diu hieu xam thyc tuy chua dang kd d mep vao canh banh cdng tac tai tdc dp n = 1.500 v/ph.
- c i n ban chd van hanh d tdc dp vdng quay tren 2.000 v/ph khi ma xam thyc bit dau phat trien rpng tren be mat canh.
Kdt qua md phdng gdp phin lam ro dae didm xam thyc trong thidt hi day kieu dng phun va ung dyng trong cai thien thidt kd dang thidt bj nay. Kdt qua hien tai ciing la c a sd dd phat trign hudng nghien ciiu nhim chii ddng ve cdng nghe va thiet ke trong nudc.*>
Ngay nhan bai: 18/4/2015 Ngay phan bien: 14/5/2015
Tai lifu tham khao:
[]]. John Allison etal; Marine waterjet propulsion, SNAME transaction. Vol. 101, 1993, pp. 275-335.
[2]. Norbert Willem Herman Bulten; Numerical Analysis of a Waterjet Propulsion System, Printservice Technische Universiteit Eindhoven, ISBN-10: 90-386-2988-5, 2006.
[3]. Marco Altosole et al; Dimensionless Numerical Approaches for the Performance Prediction of Marine Waterjet Propulsion Units, Intemational Joumal of Rotating Machinery, vol. 2012, Article ID 321306,2012.
[4]. Bonamti D, Zangeneh M, Aarlojarvi R, Eriksson J. Parametric Design of a Waterjet Pump by Means of Inverse Design, CFD Calculations and Expenmental Analyses, ASME. J. Fluids Eng., 132(3), 2010.
[5]. Jie Dang, Runwen Liu and Christiaan Pouw; Waterjet System Performance and Cavitation Test Procedures, Third Intemational Symposium on Marine Propulsors smp'13, Tasmania, Australia, May 2013, pp. 87-96.
[6]. A.A. Lomakin;fiom lytdm vd bam hu&ng true,'HXB. Khoa hpc Ky thuat, 1971.
[7]. Ansys -Fluent guide 14.5 (Theory and Tutorial).
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