Numerical simulation of water flow in an axial flow pump with adjustable guide vanes

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1 Journal of Mechancal Scence and Technology 4 (4) (010) 971~976 DOI /s z Numercal smulaton of water flow n an axal flow pump wth adjustable gude vanes Zhongdong QIAN 1, Yan WANG 1, Wenxn HUAI 1 and Youngho LEE,* 1 State Key Laboratory of Water Resources and Hydropower Engneerng Scence, Wuhan Unversty, Wuhan 4007, P. R. Chna Dvson of Mechancal and Informaton Engneerng, Korea Martme Unversty, Busan , Korea (Manuscrpt Receved May 5, 009; Revsed November 6, 009; Accepted December 1, 009) Abstract A new adjustable gude vane (AGV) s proposed n ths paper. Ths vane can reduce hydraulc losses and mprove the performance of an axal flow pump. The formula of AGV adjustment was obtaned after theoretcal analyss. The flud flow nsde the axal flow pump wth a fxed gude vane and adjustable gude vane was smulated. The calculated Q-H curves for the fxed gude vane agreed well wth the expermental ones. The results show that the attack angle and flow separaton have an mportant contrbuton to the vortces whch create hydraulc losses n the gude vane channel. The AGV can decrease hydraulc losses and sgnfcantly enhance the pump head and effcency by changng the gude vane angle. Keywords: Adjustable gude vanes; Axal flow pump; Hydraulc performance; Numercal smulaton Introducton Wth the ncreasng applcaton of an axal flow pump, the mprovement of ts effcency contnues to become more and more mportant. One of the most useful methods to ncrease ts effcency s the nstallaton of a gude vane behnd the pump mpeller [1]. Gude vanes can mprove the head and effcency of the pump by transformng the knetc energy of the rotatng flow, whch has a tangental velocty component, nto pressure energy. When the pump s workng under offdesgn condton, the attack angle, whch causes hydraulc loss, wll always exst at the leadng edge of the gude vane. Ths s because the tradtonal gude vane s fxed on the gude vane hub wth a fxed angle for the desgn condton and cannot be adjusted wth the change n workng condtons. Studes have shown that the fxed gude vane can generally retreve about 10% of the knetc energy []. Ths paper proposes a new adjustable gude vane whch can reduce hydraulc loss and mprove the performance of the axal flow pump through adjustment of the gude vane angle under off-desgn condtons. The nternal flow feld of the axal flow pump s dffcult to measure due to rotor-stator nteracton. Thus, Computatonal Flud Dynamcs (CFD) has been an effectve tool n studes on Ths paper was recommended for publcaton n revsed form by Assocate Edtor Won-Gu Joo * Correspondng author. Tel.: , Fax.: E-mal address: lyh@hhu.ac.kr KSME & Sprnger 010 the nternal flow feld n pumps and turbnes [-7]. In ths paper, the three-dmensonal steady turbulent flow nsde the full passage of a model axal flow pump was smulated usng CFD. A comparson of the computatonal head and expermental head was conducted to verfy the mathematcal model. The nfluence of AGV on the head, effcency, and energy character was analyzed, and the theorem for adjustng the AGV angle was gven.. Physcal model The model axal flow pump mpeller for ths computaton s ZM60. The computatonal doman s the flow passage from the nlet to the outlet, ncludng the mpeller and gude vanes as shown n Fg. 1. There were four mpeller blades. The dameter of the mpeller was 0.m, the hub rato 0.51, the rated speed was 1450r/mn, and the number of gude vane blades was fve. All these structures are shown n Fg.. The structured mesh was used for the nlet and outlet, whle the unstructured mesh was used for the mpeller and gude vanes due to ther complcated geometry. The total number of cells s about one mllon. The mesh of the model s shown n Fg... Mathematcal model The three-dmensonal Reynolds-averaged Naver-Stokes equatons for uncompressble flow are as follows [8]:

2 97 Z. Qan et al. / Journal of Mechancal Scence and Technology 4 (4) (010) 971~976 Fg. 4. Schematc dagram of the blade settng angle. Fg. 1. The whole flow passage axal flow pump model. Fg.. The mpeller and gude vane. Fg. 5. Comparson of the Q-H curve. where the model constants were chosen from Ref. 10. For the RNG k ε model, the Reynolds stress can be wrtten as u u j u τ j = µ t + ρ k + µ t δj xj x x (5) Meanwhle, the turbulent knetc vscosty coeffcent can be wrtten as k µ t = ρc µ (6) ε Fg.. The mesh of the model. ρ + = t x ( ρu ) 0 ( ρu ) ( ρuu j) p u τ j + = + µ + t xj x x j x j xj (1) () ' ' where τj = ρuu j s the Reynolds stress. The k ε model was chosen to enclose the equatons. Consderng the rotatng flow nsde the pump mpeller, the RNG k ε model, whch s adaptve for strongly rotatng flow, was used n ths smulaton [9, 10]. ( ) ( ) ρk ρ ku µ t k + = µ + + Gk + ρε t x xj σ k xj * ( ρε ) ( ρε ) µ ε ε u t k C1 ε + = µ + + G k C ερ t x xj σε xj k k () (4) All smulatons were conducted usng the commercal CFD software Fluent 6.. The SIMPLEC algorthm was used for the pressure-velocty couplng [11, 1]. The second order upwnd dfference scheme was used for the momentum, turbulent knetc energy, and dsspaton rate equatons. The mass flow rate was defned for the nlet and the statc pressure for the outlet. The roughness heght of the hub and casng was also consdered [1]. The sldng mesh model was used to smulate the rotor-stator nteracton n the pump. In the sldng mesh technque provded by Fluent 6., the nterface zones of adjacent cell zones were assocated wth one another to form a "grd nterface.'' The two cell zones move relatve to each other along the grd nterface. 4. Results and dscussons Seven operatng ponts for the +4 and +8 of the bladesettng angle wth the fxed-gude vanes were computed to

3 Z. Qan et al. / Journal of Mechancal Scence and Technology 4 (4) (010) 971~ Table 1. Computatonal ponts and the correspondng angle for the +4 blade settng angle. Q (m /s) α ( ) α ( ) Table. Computatonal ponts and the correspondng angle for the +8 blade settng angle. Fg. 6. Schematc dagram of AGV adjustment. valdate the mathematcal model. Fg. 4 shows the bladesettng angle, whch s determned by angle φ between the tangent to the blade meanlne and the drecton of the nlet relatve velocty w 1 at the front-edge pont of the blade. Angle φ = 0 was assumed as the mpeller desgn angle. The computatonal results of the flow dscharge (Q)-head (H) curves and the expermental ones are shown n Fg. 5. Fg. 5 shows that the computatonal results agree well wth the expermental ones, wth a maxmum error of less than 5%. The dfference comes from the tp clearance flow whch was not consdered n ths computaton at large dscharge condton [14]. The desgn of gude vanes s usually amed at mprovng flow pattern and reducng hydraulc loss by convertng some of the knetc energy nto pressure energy. Therefore, the nlet flow angle of the vane should be consstent wth the outlet flow angle of the mpeller blade at desgn condton. However, the consstency cannot be mantaned at off-desgn condtons because of the varaton of the outlet flow angle of the mpeller. The angle of attack of the gude vane s not zero, and the hydraulc loss ncreases. Adjustable gude vanes (AGV) are ntended to change the vane angle to mantan the shock free flow pattern. The schematc dagram of AGV s shown n Fg. 6. The basc dea of the AGV s that the gude vane nlet flow angle α should be adjusted accordng to the mpeller outlet flowng angle α to reduce shock loss. α can be derved from the velocty trangle when the blade angle and dscharge are known. As shown n Fg. 6, u s the crcular velocty, v s the outlet absolute velocty, w s the outlet relatve velocty, α s the outlet absolute flow angle, β s the outlet relatve flow angle, α s the desgn fxed gude vane nlet flow angle, and α s the ratonal gude vane nlet flow angle. The computatonal secton s a cylndrcal secton at the tp of the blade whose radus s equal to 0.15m. The formula of α can be derved from the velocty trangle and dscharge as follows: 60Q α = arctan π ( R r ) Rn 60 Q cot β where Q s the dscharge, R s the radus of the pump shell (7) Q (m /s) α ( ) α ( ) Fg. 7. Comparson of the Q-H curves. Fg. 8. Comparson of the Q-η curves. at the mpeller outlet, r s the hub radus, and n s the mpeller speed. Accordng to the prncple of gude vane desgn, the formula of the ratonal gude vane nlet flow angle α can be wrtten as follows [15]: α tanα = arctan ψ zsu where ψ = 1 ; Z s the blade number of the gude vane; Dπ D s the dameter of the computatonal secton; and s u s the crcumferental drectonal thckness of the gude vane nlet. The angle devaton s α = α α. In ths computaton, 0 the desgn α s known as α = The angle devaton (8)

4 974 Z. Qan et al. / Journal of Mechancal Scence and Technology 4 (4) (010) 971~976 (a) Flow pattern wth FGV (b) Flow pattern wth AGV Fg. 9. Flow pattern at the mnmum flow condton of +4 blade settng angle. (a) Flow pattern before adjustment (b) Flow pattern after adjustment Fg. 10. Flow pattern at the maxmum flow condton of +4 blade settng angle. (a) Flow pattern before adjustment (b) Flow pattern after adjustment Fg. 11. Flow pattern at the mnmum flow condton of +8 blade settng angle. α for each operatng pont s shown n Tables 1 and. Based on the full passage computaton of the axal flow pump wth fxed gude vanes (FGV) and AGV, the Q-H curves and Q-η (effcency) curves are shown n Fgs. 7 and 8. The results show that the AGV was more effcent n mprovng the performance of the axal flow pump than the FGV at off-desgn condton. For the +4 blade settng angle, the head ncreased by 0.1 m, whle the effcency ncreased by 1.178% at the mnmum dscharge condton. At the maxmum dscharge condton, t ncreased by 0.47 m and.089%, respectvely. For the +8 blade settng angle, the head ncreased by m, whle the effcency ncreased by 1.9% at the mnmum dscharge condton and m and.165%, respectvely, at the maxmum dscharge condton. The flow patterns n the gude vane channel at mnmum and maxmum dscharge condtons are shown n Fgs. 9 to 1. These fgures show that the vortces appeared at the talng edge of the fxed gude vane at low dscharge condton, whle the flow separaton appeared at the leadng edge at large dscharge condton. The vortex and flow separaton are known

5 Z. Qan et al. / Journal of Mechancal Scence and Technology 4 (4) (010) 971~ (a) Flow pattern before adjustment (b) Flow pattern after adjustment Fg. 1. Flow pattern at the maxmum flow condton of +8 blade settng angle. as the man contrbutors of hydraulc losses. The vortex and flow separaton were caused by dfferent attack angles at dfferent dscharges. Wth the applcaton of AGV, the attack angle of the gude vane s almost zero. The vortex and flow separaton caused by the attack angle dsappeared, and flow pattern mproved accordngly. As a result, the hydraulc losses caused by the vortex and flow separaton were decreased, and the head and effcency of the axal flow pump was enhanced. 5. Concluson Smulatons of the three-dmensonal steady flow n an axal flow pump wth FGV and AGV were conducted usng the commercal CFD software Fluent 6.. The results show the followng: (I) The mathematcal model used n ths paper can accurately smulate the flow feld nsde the axal flow pump. The computatonal Q-H curves agree well wth the expermental ones. (II) The theorem of AGV adjustment was deduced from the mpeller outlet velocty trangle and the prncple of gude vane desgn. (III) The AGV can reduce the negatve nfluences of attack angle and mprove the flow pattern n the gude vane channel effectvely, sgnfcantly decreasng hydraulc loss. (IV) The AGV can sgnfcantly mprove the head and effcency of the pump at off-desgn condtons. In ths smulaton, the maxmum mprovement of the head and the effcency were m and.089%, respectvely. Acknowledgements Ths work was funded by the Natonal Nature Scence Foundaton of Chna (Grant No ). Nomenclature D H n Q : Dameter [m] : Head [m] : Revoluton per mnute [rpm] : Flow rate [m /s] R : Radus of the pump shell at the mpeller outlet [m] r : Hub radus [m] S : Crcumferental drectonal thckness of the gude vane nlet [m] t : Tme [s] u : Crcular velocty [m/s] v : Absolute velocty [m/s] w : Relatve velocty [m/s] Z : Blade number of the gude vane α : Flow angle [deg] β : Relatve flow angle [deg] η : Effcency ρ : Densty [kg/m ] φ : Blade settng angle [deg] ψ : Crowdng coeffcent Subscrpts 1 : Inlet of blade : Outlet of blade : Inlet of gude vane References [1] J. Hu, S. Huang and P. S. Wang, Research on hydrodynamc characterstcs of axal waterjet pump wth gude vane. Journal of Hydroelectrc Engneerng, (008) -6. [] F. P. Tang and G. Q. Wang, Influence of Outlet Gude Vanes upon Performances of Water jet Axal-Flow Pump. Journal of Shp Mechancs, 6 (006) [] L. Belt and T. Cousot, Sem-Spral Casng and Runner Naver-Stokes Smulaton for a Refurbshment Project. Proc, of the 19th the LAHR Symposum. Sngapore, (1998) [4] F. J. Wang, Y. J. L and Y. L. Wang, CFD Smulaton of D flow n large-bore axal-flow pump wth half-elbow sucton sump. Journal of Hydrodynamcs, 18 () (006) [5] Blanco M. Numercal flow smulaton n a centrfugal pump wth mpeller-volute nteracton. ASME 000 Flud Engneerng Dvson Summer Meetng, Boston, Massachusetts, June, (000) [6] S. N. Shukla and J. T. Kshrsagar. Numeral experments on

6 976 Z. Qan et al. / Journal of Mechancal Scence and Technology 4 (4) (010) 971~976 a centrfugal pump.asme Fluds Engneerng Dvson (Publcaton) FED, 57 (B) (00) [7] H. X. Chen. Research on turbulent flow wthn the vortex pumps. Journal of Hydrodynamc: Ser B, 16 (6) (004) [8] B. E. Launder and D. B. Spaldng. The Numercal Computaton of Turbulent Flows. Computer Methods n Appled Mechancs and Engneerng, (1974) [9] Z. Wang and W. M. Lu, Two Modfcatory K-ε Turbulence Models for Turbulent Swrlng Flows. Journal of Hydrodynamcs, (00) [10] Y. Vctor and O. Steven, A. Renormalzaton group analyss of turbulence : basc theory.journal of Scentfc Computng, 1 (1) (1986) -11. [11] S. V. Patanker, Numercal heat transfer and flud flow. Hemphere, Washngton, (1980) [1] S. V. Patanker and D. B. Spaldng, A calculaton procedure for heat, mass and momentum transfer n three-dmensonal parabolc flows.int J Heat Mass Transfer, 15 (197) [1] M. Ishda, D. Sakaguch and Z. Sun. Suppresson of rotatng stall n vaneless dffuser by wall roughness control. Proceedngs of the nternatonal Conference on Pumps and Fans.ICPE, (1998) -41. [14] M. Yaras, Y. K. Zhu and S. A. Sjolander, Flow feld n the tp gap of a planar cascade of turbne blades.asme Journal of Turbomachnery, 111 () (1989) [15] X. F. Guan, Modern pump techncal manual. Bejng: Chna Astronautcs Publshng House, (1995) -5. Zhong-Dong Qan s a Professor at the School of Water Resources and Hydropower Engneerng at Wuhan Unversty, Chna. He receved hs Ph.D. degree n Thermal Engneerng from Northern Eastern Unversty n 00. He has research experence from 00 to 004 at Tsnghua Unversty as a postdoctoral researcher. Hs teachng and research areas nclude computatonal flud dynamcs, hydraulc machnery and hydrodynamcs. Young-Ho Lee receved hs B.E. and M.E. degrees from Korea Martme Unversty, Korea. He receved hs Ph.D. n Engneerng from the Unversty of Tokyo, Japan. Dr. Lee s currently a Professor at the Dvson of Mechancal and Informaton Engneerng, Korea Martme Unversty. Hs research nterests nclude ocean energy, wnd energy, small hydro power, flud machnery, PIV, and CFD.