Performance analysis of axial flow pump on gap changing between impeller and guide vane

Transcription

1 IOP Conference Seres: Materals Scence and Engneerng OPEN ACCESS Performance analyss of axal flow pump on gap changng between mpeller and gude vane To cte ths artcle: W J Wang et al 2013 IOP Conf. Ser.: Mater. Sc. Eng Vew the artcle onlne for updates and enhancements. Related content - Development and numercal analyss of low specfc speed mxed-flow pump H F L, Y W Huo, Z B Pan et al. - Study on mprovement of hump characterstc of an axal flow axal pump by groovng nlet wall K F Yang, J J Feng, G J Zhu et al. - Backflow vortex behavours n contrarotatng axal flow pump at low flow rates D Zhang, T Tsuneda, Y Katayama et al. Ths content was downloaded from IP address on 03/10/2018 at 17:29

2 Performance analyss of axal flow pump on gap changng between mpeller and gude vane W J Wang, Q H Lang,Y Wang,Y Yang,G Yn and X X Sh Research Center of Flud Machnery Engneerng and Technology, Jangsu Unversty, Zhenang , Chna E-mal: lqh0321@163.com Abstract. In order to study the nfluence on gap changng of the statc and dynamc components n axal flow pump, the axal flow pump model (TJ04-ZL-06) that used n the eastern of south-to-north water dverson proect was selected. Steady turbulence feld wth dfferent gaps was smulated by standard κ ε turbulence model and double-tme steppng methods. Informaton on the pressure dstrbuton and velocty dstrbuton of mpeller surfaces were obtaned. Then, calculated results were compared wth the test results and analyzed. The results show that the performance of pump s not senstve wth the axal gap wdth under desgn condtons and the large flow rate condton. Wth ncreasng gap wdth, t wll be mproved n low flow rate condton. The attack angle of mpeller nlet n small flow rate condton become small and the flow separaton phenomenon can be observed n ths condton. The axal velocty dstrbuton of mpeller outlet s nonlnear and to ncrease the axal gap s to mprove the flow pattern near the hub effectvely. The trend of calculatng results s dentcal wth test. It wll play a gudng role to the axal pump operaton and desgn n south-to-north water dverson proect. 1. Introducton Axal flow pump s a low head pump and s wdely appled n rrgaton, muncpal water supply and dranage, water dverson works, power plant crculatng water proects. In recent years, t have also been appled n nuclear power, et propulson, etc. Flow components nclude nlet, mpellers, vanes and outlet. The performance of the varous hydraulc components affect hydraulc performance of the pump. A lot of research have been done by domestc and foregn scholars. Kochevsky AN etc.[1] analyzed nternal axal flow of axal flow pump wth back gude vane by usng CFD software. Zerke WC[2] studed flow characterstcs and testng technques of the tp clearance n hgh Reynolds axal flow pump. In order to study the varaton and relatonshps of nternal pressure pulsaton and nose n axal flow pump n dfferent condtons,wang Hongguang etc.[3] smulated the dstrbuton of flow feld and sound feld n axal flow pump by usng numercal smulaton, computatonal flud dynamcs software and acoustc software, and analyss the tme doman and frequency doman by settng the unsteady pulse power of vanes as sound source, and comparatvely analyzed the dfference of acoustc feld dstrbuton between the pumps wth and wthout Content from ths work may be used under the terms of the Creatve Commons Attrbuton 3.0 lcence. Any further dstrbuton of ths work must mantan attrbuton to the author(s) and the ttle of the work, ournal ctaton and DOI. Publshed under lcence by IOP Publshng Ltd 1

3 pump casng vbraton by usng the boundary element method. Huang Huanmng etc.[4] conducted numercal smulaton for axal mpeller flow feld on the commercal software CFX platform, and compared relatve speed and streamlne dstrbuton of the 90% mpeller outlet heght and root poston wth PIV measurement results obtaned relatve speed and streamlne the n and are compared, and verfed the valdty of the numercal smulaton. L Zhong, etc.[5] measured the outlet flow feld of three condtons of a axal flow pump by usng a sphercal fve-hole probe and obtaned the dstrbuton of crcumferental, radal velocty component of mpeller outlet absolute velocty and velocty crculaton. Currently, the study on the gap between mpeller outlet and gude vanes of axal flow pump s not enough, the velocty feld, pressure feld are not been studed well, especally movement couplng between the mpeller and gude vane. Thus, ths paper carred a full flow passage steady turbulent flow calculaton for axal flow pump and compared the external characterstcs of unsteady calculaton for dfferent gaps wth expermental results, the velocty feld wthn dfferent axal clearance was analyzed on ths bass. 2. Unsteady calculatons 2.1. Steady turbulent equatons Lqud flow patterns follow three conservaton laws. Namely the conservaton of mass, momentum and energy. Unsteady flow s solved by second-order mplct tme steppng method, and standard κ-ε turbulence model was chosen from turbulence model[6,7],and the full three-dmensonal flow feld of 0.6Q d,0.8 Q d,1.0 Q d and 1.2 Q d was calculated. Under the relatve coordnate system of constant rotatng angular velocty ω, and the nternal flow of axal flow pump s three-dmensonal, steady, ncompressble flow, the basc tme-averaged movement equaton s as follow: u x 0 (1) u u ( t ) ( u x u ) P x x x x S where: u u - the average velocty component, x x - coordnate component, P pressure, μ μt - flud vscosty and turbulent vscosty, S - generalzed source term. Standard k-ε model s the most commonly used assumptons whch based on eddy vscosty turbulence model. Turbulent knetc energy equaton (k equaton) and the turbulent dsspaton rate equaton (ε equaton) are as follows: (2) ( ku ) x x ( u ) x x t k Pk k x t ( c1pk c2) x k where: turbulent knetc energy and turbulent dsspaton rate are as follows: (3) (4) k 1 2 ' ' u u, u x u x (5) Turbulent vscosty s: 2

4 P k s the pressure generated tem caused by velocty gradent: u u u P k t x x x Model parameters are:σ k =1.0,σ ε =1.3,c 1 =1.44,c 2 =1.92,c μ = k t c (6) 2.2. Computatonal doman of axal flow pump The excellent axal flow pump model (TJ04-ZL-06) of Tann same table test of South-to-North Water Dverson Proect presded by Mnstry of Water Resources was chosen as the research obect. Ths model was appled n the Lushandatao Pumpng Staton of Eastern Route of South-to-North Water Transfer Proect, the nomnal specfc speed s The man desgn parameters are as follows: the flow rate Q d =350L/s, the head Hd=4.6m, rotatonal speed n=1450rpm. The man geometrc parameters are as follows: mpeller dameter D2=300mm, hub dameter dh=120mm, mpeller blades zr=3, the gude vane blades zs=5. Impeller and gude vane shapes are shown n fgure 1 (a) (b),the water body of whole computatonal doman s shown n fgure 1 (c), Axal clearance s shown n fgure 1 (d), and 40mm was chosen as the axal spacng s between mpeller outlet and gude vne. (7) (a) mpeller (b) gude vne (c) the water body of computatonal (d) the axal spacng s doman Fgure 1. 3D model of mpeller and gude vane 2.3. Boundary condtons and mesh processng In order to obtan more stable flow, the length of water taken straght ppe s chosen as 3 tmes of the outer dameter of mpeller. Lqud has been fully developed nto a turbulent state when enterng n the mpeller. The nlet boundary condtons of computatonal doman was chosen as velocty nlet. The velocty of nlet s axal and symmetrc. The sze s determned by the flow rate of workng condtons. The standard atmospherc pressure was chosen as the reference pressure of nlet. Outlet was chosen as the boundary condton of outlet. The calculaton llustrate that backflow phenomenon mght occur at run-tme of axal flow pump at outlet. In order to mprove the stablty of computaton [8-10], standard wall functon was chosen at the near-wall regon and the approprate wall roughness should be set dependng on the crcumstances. Accuracy of calculaton results was set as Structured grd was chosen for computatonal grd, whch wth the characterstcs of orderly arrangng, 3

5 clear structure and excellent mesh qualty. For the flow feld of axal spacng for axal flow pump movement component, the ptch s small when comparng wth the whole machne, the results by numercal smulaton wth the structured grd can reflect the true flow pattern of axal spacng better. The flow components structured grd shown n fgure 2. Wth the mprovement of grd qualty, performance predcton errors wll reduce gradually. grd-ndependent nspecton was done when meshng n ths paper. Takng nto the computatonal precson and economy[13-14], 1,105,046 was chosen as the number of computatonal grds. (a) Structured grd (b) The grd of mpeller water body Fgure 2. Calculatng mesh (c) The grd of gude vne water body 3. Calculaton results Under the four typcal axal flow pump condtons of hgh flow rate condtons (1.2 Q d ), desgn condtons (1.0 Q d ) and low flow condtons (0.6 Q d, 0.8 Q d ), axal spacng was changed (10,20,30, 40mm) to study the nsde flow of pump, the workng flud s water (densty ρ take 1000kg/m 3 ) The effects axal spacng values have on the outer characterstcs of model pump The curve of flow capacty-head and curve of flow capacty-head that under dfferent axal spacng s shown n fgure 3. As s shown n fgure 3, the axal clearance senstvty from head and effcency s low n the large flow rate condton. The head ncrease wth the decrease of axal clearance at the low flow rate condton that around the hump, the where s s 10mm, the head s 6.95m, ths s the smallest dfference wth the expermental values. When s s 40mm, the head s only 6.32mm. The predcton of effcency s not accurate at the small flow rate workng condton, the dfference can be as much as 20%, especally when s s 40mm. Ths s because the secondary flow of the mpeller surface at low flow rate workng condton and nlet attack angel devate from optmum operatng condton [11]~[12]. The effcency ncrease when the axal clearance reduce. Calculaton results share the same tendency wth the expermental outer characterstc curve. The numercal smulaton results predcted the performance axal flow pump accurately. (a) curve of flow capacty-head (b) curve of flow capacty-head Fgure 3. Performance curves of smulaton and test 4

6 3.2. Analyss of physcal quanttes at the md-secton To analyze the change law of physcal quanttes n dfferent axal gap, the physcal parameters of the ntermedate secton s/2 was analyzed. The cloud pctures of pressure and velocty vector of the axal gap ntermedate secton s/2 was shown n fgure 4 and fgure 5. As s shown n fgure 4, the mnmum and maxmum of pressure was alternatng at the mddle secton. There are 5 maxmum pressure area, the same as the number of gude vnes. These area s affected by gude vnes, the maxmum pressure area decreased wth the ncrease of axal gap. Thus, the ncrease can decrease the nlet pressure of gude vnes. As s shown n fgure 5, the velocty gradent of ntermedate secton decreased wth the ncrease of axal spacng. As s n fgure 4, the mnmum and maxmum of pressure was alternatng at the mddle secton. The maxmum of velocty shown at the edge. The velocty of hub s small, the crcular moton s obvous. Fgure 4. Pressure vector contour of z=s/2 surfaces under 1.0Q d condton Fgure 5. Velocty vector contour of z=s/2 surfaces under 1.0Q d cond 3.3. The effects axal spacng have on mpeller The relatve velocty of the near nlet area s hgh and the pressure s low. The energy loss caused by the vortex that occurred at the gap by the nteracton of gude vanes and blades. Consderng the movement component spacng s very mportant to the relatve velocty dstrbuton of the workng face of vnes when desgnng an axal flow pump. The velocty vector dstrbuton of vnes workng face from dfferent workng condtons s shown n fgure 6, fgure 7 and fgure 8. As s shown n fgure 6, velocty gradent varaton s obvous n certan part of head and tal of vnes under low flow rate condtons. The velocty gradent reduced wth the ncrease of the axal gap. The maxmum of the mpeller surface speed s 24.92m/s. The maxmum velocty gradent area of head and tal s also shown n fgure 7 and fgure 8. Wth the ncrease of flow rate, the flow around the hub strengthened and reached the maxmum velocty, the mnmum velocty shown around the hub. The mnmum velocty area of all workng condtons ncreased wth the ncrease of axal gap. Fgure 6. Velocty vector contour of mpeller surfaces under 0.6Q d condton 5

7 Fgure 7. Velocty vector contour of mpeller surfaces under 1.0Q d condton Fgure 8. Velocty vector contour of mpeller surfaces under 1.2 Q d condton 3.4.The effects varaton of axal spacng have on axal velocty of mpeller outlet The axal velocty dstrbutons of mpeller outlet of dfferent workng condton and dfferent axal spacng are shown n fgure 9. R s the mpeller radal dmenson, the R of hub s 60mm and the R of shroud s 150mm. As s shown n fgure 9, the tendency of the axal velocty dstrbutons of mpeller outlet of dfferent workng condton and dfferent axal spacng are smlar. The axal velocty of mpeller outlet change monotonously from the hub to the shroud under desgn condton and large flow rate condton. The axal velocty dstrbuted lnearly. The effects varaton of axal spacng have on axal velocty dstrbuton s small. The effects varaton of axal spacng have on axal velocty dstrbuton of mpeller outlet s obvous under low flow rate condton. It dstrbuted nonlnearly [S]~[17]. The axal spacng of mpeller outlet and vnes nlet are mportant parameters n axal flow pump desgn. It affect the pump performance and flow feld characterstcs. The ncrease of axal spacng can mprove the flow n mpeller and gaps. (a) Q/Q d =0.6 (b) Q/Q dt =0.8 (c) Q/Q d =1.0 (d) Q/Q d =1.2 Fgure 9.Axal velocty of mpeller outlet under dfferent condtons and dfferent gap 4.conclusons The commercal CFD software ANSYS CFX was used n ths paper. The axal flow pump model(tj-zl-06) wth the namely specfc speed of 1000 was chosen. The test data of from the Tann same table test of South-to-North Water Dverson Proect presded by Mnstry of Water Resources was selected. The effects varaton of axal spacng of dfferent movement component have on performance of axal flow pump have calculated. The calculatons are as follows: 1) The effects axal spacng of movement component have on performance of axal flow pump s 6

8 small under desgn condton and large flow rate condton. The effect of small flow rate condton s obvous. The approprate ncrease of the gap of mpeller outlet and gude vnes nlet can mprove the flow of movement component under low flow rate condton effectvely. 2) Fve maxmum and mnmum areas of pressure was alternatng at the mddle secton of axal spacng. It s equal to the number of gude vnes. The rule can also apply to velocty. The flow n ths area was nterfered mghtly by the gude vnes. 3) The mpeller outlet axal velocty dstrbuton s nonlnear under low flow rate condtons. The mpeller outlet axal velocty dstrbuton s approxmate lnear under desgn and large flow rate condtons. The approprate ncrease of axal spacng can mprove the flow around the hub effectvely. Acknowledgements The present study was supported fnancally by Natonal Scence and Technology Support Program (2011BAF14B01), a Proect Funded by the Prorty Academc Program Development of Jangsu Hgher Educaton Insttutons (PAPD, BK ) and Graduate Tranng Innovaton Proect of Jangsu provnce(cxlx13_662), Chna. Ther gudance and assstance are gratefully acknowledged. The authors would lke to express ther apprecaton to Professor Janru Lu, of Research Center of Flud Machnery Engneerng and Technology, Jangsu Unversty, Zhenang, Jangsu, Chna, for hs valuable comments and suggestons. References [1] Kochevsky A N, Kozlov S N, Aye K M, et al Measurements of the tp clearance flow for a hgh-reynolds-number axal-flow rotor-part 2: Detaled flow measurements Proc. ASME FEDSM (Houston, USA,19-23 June 2005) p 1397 [2] Zerke W C, Farrell K J, Straka W A 1994 Amercan Socety of Mechancal Engneers [3] Wang H G, Xu X L, Yang A L, et al J. Dran. Irrg. Mach. Eng. 29(3) [4] Huang Huanmng 2009 J. of Shangha Jaotong Unversty 43(1) [5] L Z, Yang M G, Wang X K 2009 J. Dran. Irrg. Mach. 27(1) [6] Sh W D, Zhang H, Chen B, et al J. Dran. Irrg. Mach. Eng. 28(5) [7] Sumo S, Masahro S, Hdeo F, et al J. of Themal Scence 16(4) [8] Wang F J, Zhang L, L Y J, et al Chn. J.Mech. Eng. 44(8) [9] Kaya D 2003 J.Energy Converson and Management 44(11) [10] Qu B Y, Lu C, Yuan W S 2000 J. Mech. Eng. 36(7) [11] Yang C X, Du Y Y, L Y B 2011 J. Dran. Irrg. Mach. Eng. 30(5) [12] Yang Q F, Wang Y S, Zhang H Z, et al J. Mech.l Eng. 45(6) [13] Sh W D, Zhang D S, Guan XF, et al Chn. J. Mech. Eng. 23(1) [14] Feng W M, Song L, Zuo L, et al J. Dran.Irrg. Mach. Eng. 28(6)