Simulation and experiment of the effect of clearance of impeller wear-rings on the performance of centrifugal pump

Transcription

1 IOP Conference Seres: Earth and Envronmental Scence Smulaton and experment of the effect of clearance of mpeller wear-rngs on the performance of centrfugal pump To cte ths artcle: S X Chen et al 01 IOP Conf. Ser.: Earth Envron. Sc Related content - Research on the effect of wear-rng clearances to the performance of centrfugal pump W G Zhao, Y B L, X Y Wang et al. - Effects of computatonal grds and turbulence models on numercal smulaton of centrfugal pump wth CFD H L Lu, M M Lu, L Dong et al. - Applcablty of eddy vscosty turbulence models n low specfc speed centrfugal pump Y Wang and W J Wang Vew the artcle onlne for updates and enhancements. Ths content was downloaded from IP address on 9/04/018 at 08:9

2 6th IAHR Symposum on Hydraulc Machnery and Systems IOP Conf. Seres: Earth and Envronmental Scence 15 (01) IOP Publshng do: / /15/7/07017 Smulaton and experment of the effect of clearance of mpeller wear-rngs on the performance of centrfugal pump S X Chen, Z Y Pan, Y L Wu and D Q Zhang Research Center of Flud Machnery Engneerng and Technology, Jangsu Unversty, Zhenjang, Jangsu Provnce, 1013,Chna E-mal: chenshxngboy@163.com Abstract The effect of clearance of mpeller wear-rngs on the performance of a centrfugal pump was nvestgated numercally and expermentally. The whole flow feld model ncludng front and back shrouds of pump was desgned so as to accurately calculate the head and effcency of the centrfugal pump. Based on RNG k-ε turbulence model, three wear-rngs schemes were establshed, and the effects of clearance of mpeller wear-rngs on the hydraulc effcency and mechancal effcency of the centrfugal pump was analyzed, chefly from the turbulent knetc energy, vortcty and radal force angles. Accordng to the results, t can be drawn that the head and total effcency of the centrfugal pump ncrease as the clearance value of wear-rngs narrows. The followng reasons may account for t: frstly, as the clearance value of wear-rngs declnes, the turbulent knetc energy and energy dsspaton decrease wthn the mpeller, and the mpact of secondary flow at the nlet of mpeller on the manstream weakens slowly, whch leads to a lower hydraulc loss, thus a hgher hydraulc effcency; secondly, radal force decreases wth the clearance value of wear-rngs, so the eccentrc whrl of centrfugal pump s dampened, whch results n a lower mechancal loss and a hgher mechancal effcency; thrdly, the front shroud leakage dmnshes wth the clearance value of wear-rngs, therefore, the volume loss s reduced and volume effcency mproved. Fnally, the frst wear-rng scheme of mpeller s adopted after comprehensve comparson of these three wear-rng schemes, because ts effcency s hghest and t satsfes the requrements of the engneerng applcaton. 1. Introducton The clearance of mpeller wear-rngs n a centrfugal pump wll lead to volume loss, and meanwhle change the nternal flow regmes of centrfugal pump. Consequently, t has an essental effect on the external characterstcs of centrfugal pump. But the clearance sze of wear-rngs s relatvely small, where the flow s very complex, and relatvely dffcult to research. Usually, the expermental method s avalable to study the effect of wear-rngs clearance on the external characterstcs of centrfugal pump, and numercal smulatons based on CFD generally gnore the exstence of the clearance of wear-rngs. Above all, t s very meanngful to ntensvely nvestgate the nternal and external characterstcs of centrfugal pump consderng the clearance of wear-rngs both numercally and expermentally. Black, H. F. [1] researched the flud-nduced forces at the seal rng clearance of centrfugal pump theoretcally and expermentally, and ponted out that they had a sgnfcant nfluence on the vbraton of pump rotor. Tosho Hrano et al. [] nvestgated the labyrnth seal by numercal smulatons, and Publshed under lcence by IOP Publshng Ltd 1

3 6th IAHR Symposum on Hydraulc Machnery and Systems IOP Conf. Seres: Earth and Envronmental Scence 15 (01) IOP Publshng do: / /15/7/07017 analyzed the effect of leakage flow rate of seal clearance and clearance flow on the mechancal rotor. Chen Yu et al. [3] studed the mpact of clearance of wear-rngs on the performance of centrfugal ol pump whle handlng water by the experment method, and compared the dfferent nfluences of front and back wear-rngs on the performance of centrfugal pump. Besdes, other scholars [4~7] researched the effect of clearance of wear-rngs on the leakage loss and mechancal effcency of centrfugal pump, and so on. Comprehensve analyss above research works about the clearance of wear-rngs, t was found that they had focused on the effect of clearance of wear-rngs on the volume loss and mechancal loss of centrfugal pump, but usually gnored the effect of hydraulc loss, and how to dentfy the clearance n the radus drecton of wear-rngs (for short, the clearance of wear-rngs, the same below) n the runnng process of centrfugal pump s almost blank. The paper, frst, studed the effect of clearance values varaton of wear-rngs on the hydraulc loss of centrfugal pump from the turbulent knetc energy and vortcty angles; next, nvestgated the effect of clearance values varaton of wear-rngs on the mechancal loss of centrfugal pump from the radal force angle; last, ascertaned the best wearrngs scheme through the comparson of expermental and computatonal values and the error analyss of effcency, and summarzed reasons of the effect of clearance of wear-rngs on the performance of centrfugal pump.. Expermental pump and numercal method.1. Expermental pump The desgn parameters of calculated centrfugal pump mpeller are descrbed as followng: head of m, flow of 18.5 m 3 /h, specfc speed of 60.5, rotatonal speed of 3500 r/mn, mpeller nlet dameter of 53 mm, mpeller outer dameter of 155 mm, mpeller outlet wdth of 6 mm, 5 blades. The specfc datas of blade type used n the paper are from the reference [8]. Test-bed and mpeller are shown n Fgure 1... Numercal method Fgure 1. Test-bed and mpeller..1. Meshng. Accordng to the structural parameters of centrfugal pump, Pro/E software was appled to 3D modelng, and mxed wth scannng technology was adopted to the three-dmensonal entty model of mpeller and volute. Flud smulaton platform ANSYS-FLUENT n commercal software ANSYS 13.0 Workbench was used to make the CFD smulaton. Geometry areas were meshed n ANSYS ICEM CFD software, and the grd qualty nspecton was made n the numercal smulaton. The orthogonal qualty of grd was more than 0.50, and ts qualty was hgh enough to meet the calculaton requrements. Structured grds were employed to the clearance water body of mpeller wear-rngs (llustrated n Fgure (a)), unstructured grds near the major dstortons of front shroud and mpeller water bodes were locally refned (llustrated n Fgure (b), (c)) n order to mprove the accuracy of calculaton. The grd numbers of full flow feld were , and respectvely at three mpeller wear-rngs values (lsted n Table 1).

4 6th IAHR Symposum on Hydraulc Machnery and Systems IOP Conf. Seres: Earth and Envronmental Scence 15 (01) IOP Publshng do: / /15/7/07017 (a)wear-rngs grd (b) Front shroud grd (c) Impeller grd Fgure Meshng Table 1. Three mpeller wear-rngs schemes Scheme I II III Clearance value of wear-rngs/mm Governng Equaton. Accordng to the Boussnesq turbulent vortex vscous hypothess, RNG k- ε -equaton turbulence model was appled to the turbulent core of full developed turbulent flow [9, 10], and ts basc equatons as follows, Contnuty equaton follows that u 0 (1) x Momentum equaton follows that u j u u u 1 p 1 u j () t x x x k-equaton follows that ε-equaton follows that t t x j x k k x t k ku G x u x t C x j 1 G k k C k k (3) (4)..3. Boundary Condtons. Inlet boundary condton: velocty-nlet, assumng that nlet velocty was evenly dstrbuted along the axs; outlet boundary condton: outflow, havng no nfluence on the upstream; wall boundary condton: no slp wall boundary condton was used to the walls, and the standard wall functon was appled to the area near the walls. In addton, the roughness heght of the water walls was 50 μm. 3. Calculaton results and analyss 3.1. Effect of the clearance of wear-rngs on the turbulence Turbulent knetc energy s the most common physcal quantty of turbulence model, and turbulence ntensty s usually adopted to estmate turbulent knetc energy. It follows that 3

5 6th IAHR Symposum on Hydraulc Machnery and Systems IOP Conf. Seres: Earth and Envronmental Scence 15 (01) IOP Publshng do: / /15/7/ k ( ui) (5) 0.15 where I 0.16 Re, and u s average velocty, I s turbulence ntensty, Re s Reynolds number. Fgure 3 llustrates the dstrbuton of turbulent knetc energy at the axal secton of x 0 for three clearance values of wear-rngs, when Q =18.4 m 3 /h. It ndcates that the low turbulent knetc energy area gradually extends to mpeller outlet wth the decrease of clearance value of wear-rngs, whch demonstrates that the turbulent knetc energy at the mpeller axal secton s reduced wth the clearance value of wear-rngs. k/(m s - ) (a)0.1mm (b)0.3mm (c)0.5mm Fgure 3. Dstrbuton of turbulent knetc energy at the axal secton of x 0 In order to quanttatve research on the effect of clearance of wear-rngs on the turbulent knetc energy, t was calculated by surface ntegraton on the axal secton of x 0(results llustrated n Fgure 4). It shows that when the flow rate s fxed, turbulent knetc energy dmnshes wth the clearance value of wear-rngs (n accordance wth the above result obtaned by qualtatve analyss); when the clearance value of wear-rngs s unchanged, turbulent knetc energy ncreases wth the flow rate. Accordng to the formula (5), the turbulence ntensty s hgher when the turbulent knetc energy s mproved, the flud energy dsspaton s augmented and hydraulc loss s hgher. Ths shows that the turbulent knetc energy wthn the mpeller s lower as the clearance value of wear-rngs declnes, whch leads to lower turbulence ntensty and dampened flud energy dsspaton, therefore, the hydraulc loss wthn the mpeller s declned and hydraulc effcency s mproved. Fgure 4. Curves of turbulence knetc energy at dfferent wear-rngs values 4

6 6th IAHR Symposum on Hydraulc Machnery and Systems IOP Conf. Seres: Earth and Envronmental Scence 15 (01) IOP Publshng do: / /15/7/ Effect of the clearance of wear-rngs on the mpeller nlet vortcty of centrfugal pump Vortcty s the curl of velocty feld. Internal flow of centrfugal pump s relatvely complcated, and vortex flow often appears. Vortcty s usually used to measure ts sze and drecton. It s well known that second flow caused by the front shroud leakage wll mpact the manstream of mpeller nlet, and vortex wll appear at the mpeller nlet area. Fgure 5 llustrates the dstrbuton of vortcty at the axal secton of x 0 for three clearance values of wear-rngs, when Q =18.4 m3 /h. It shows that vortcty area of mpeller nlet decreases wth the clearance value of wear-rngs. It demonstrates that the number of vortex caused by the effect of second flow on the manstream s obvously lower when the clearance value of wear-rngs demnshes. Thus, the hydraulc loss caused by the mpact of second flow at the mpeller nlet wll be reduced, as a result, the hydraulc effcency wll be hgher. ω/(10 s -1 ) (a)0.1mm (b) 0.3mm (c) 0.5mm Fgure 5. Dstrbuton of vortcty at the axal secton of x Effect of the clearance of wear-rngs on the radal force To nvestgate the effect of clearance of wear-rngs on the radal force of centrfugal pump, the calculaton method about the radal force n the references [11, 1] was adopted. Radal forces on the mpeller at three clearance values of wear-rngs respectvely were calculated n the paper(results llustrated n Fgure 6). It shows that the radal force dmnshes wth the clearance value of wearrngs when the flow rate s fxed; the radal force declnes as the flow rate s augmented when the clearance value of wear-rngs s unchanged. The eccentrc whrl of mpeller aggravates due to the rse of radal force, whch causes the mprovement of mechancal loss of rotor system. That demonstrates the radal force s lower when the clearance value of wear-rngs decreases, accordngly, the eccentrc whrl of rotor s dampened and the frcton between the rotor and pump casng s weakened, whch eventually causes the reduce of mechancal loss of pump and the advance of mechancal effcency. It s n accordance wth the result obtaned by the experment n the reference [6]. Fgure 6. Curves of radal force at dfferent wear-rngs values 5

7 6th IAHR Symposum on Hydraulc Machnery and Systems IOP Conf. Seres: Earth and Envronmental Scence 15 (01) IOP Publshng do: / /15/7/ Expermental comparson and the error analyss of effcency 4.1. Expermental comparson In order to study the effect of clearance of wear-rngs on the external characterstcs of centrfugal pump, the performance experment of pump was done, and the numercal smulaton for three clearance schemes of wear-rngs was carred out (llustrated n the Fgure 7). Fgure 7 (a) shows that the calculated head values are greater than the expermental values; when the flow rate s fxed, the head ncreases as the clearance value of wear-rngs s dmnshed. Fgure 7 (b) shows that the calculated values of hydraulc effcency at the scheme of 0.1 mm are hgher than the expermental values n the small flow rate area, whle those at schemes of 0.3 mm and 0.5 mm are lower than the expermental values n the large flow rate area; the calculated values of hydraulc effcency at three schemes are greater than the expermental values n the large flow rate area; when the flow rate s unchanged, the hydraulc effcency rses wth the decrease of clearance value of wear-rngs, whch s n accordance wth the above results obtaned by the analyss of turbulent knetc energy and vortcty; n addton, the flow rate of best effcency pont at three schemes s more than that of experment. The expermental effcency s the total effcency, whle obtaned effcency numercally s the hydraulc effcency consderng the front shroud leakage flow, not fully consderng volumetrc effcency and mechancal effcency. In theory, the numercal effcency values are hgher than the expermental values. Moreover, the front shroud leakage declnes wth the clearance value of wearrngs, whch causes volume loss to be reduced and volume effcency to be augmented [6]. Above all, the scheme of 0.1 mm s most close to the realty. (a)the head-flow rate curves (b) The effcency-flow rate curves Fgure 7. Comparsons of performance curves between experment and smulaton 4.. The error analyss of effcency To quanttatve analyss on the concdence between the effcency calculaton and expermental value at three clearance schemes of wear-rngs, dstrbuton densty of ther dfference was analyzed respectvely, that was to calculate the fttng degree between the calculatons and expermental values at three clearance schemes of wear-rngs by the precson analyss method. The mathematcs model chosen to measure the accuracy was the standard devaton formula. It follows that m 1 n n 1 ( ) (6) where m s the standard devaton between the effcency calculaton and expermental value; s the th effcency calculaton; s the th effcency expermental value; n s the total number of samples, whch s taken as 10 n the paper. The calculaton results are llustrated n Table. 6

8 6th IAHR Symposum on Hydraulc Machnery and Systems IOP Conf. Seres: Earth and Envronmental Scence 15 (01) IOP Publshng do: / /15/7/07017 Table. Standard devaton of effcency at dfferent clearance values of wear-rngs Clearance value of wear-rngs /mm Standard devaton of effcency /% Table shows that the standard devaton under the scheme of 0.1 mm s mnmum, whch demonstrates that the concdence between the effcency calculaton and expermental value s hghest. Thus, the frst scheme s the best one n these three mpeller wear-rngs schemes from the hghest effcency angle. 5. Concluson 1) The head and total effcency of centrfugal pump ncrease as the clearance value of wear-rngs narrows. Three reasons may account for t: frstly, as the clearance value of wear-rngs declnes, the turbulent knetc energy and energy dsspaton decrease wthn the mpeller, and the mpact of secondary flow at the nlet of mpeller on the manstream weakens slowly, whch leads to a lower hydraulc loss, thus a hgher hydraulc effcency; secondly, radal force decreases wth the clearance value of wear-rngs, so the eccentrc whrl of centrfugal pump s dampened, whch results n a lower mechancal loss and a hgher mechancal effcency; thrdly, the front shroud leakage dmnshes wth the clearance value of wear-rngs, therefore, the volume loss s reduced and volume effcency mproved. ) Fnally, the scheme of 0.1 mm s adopted for the clearance value of wear-rngs n the radal drecton after comprehensve comparson of these three wear-rng schemes, because ts effcency s hghest. It also satsfes the scope of recommended values about the clearance value of wear-rngs n the radal drecton for the engneerng applcaton n the reference [13], whch shows that t has a certan feasblty to determne the clearance value of wear-rngs n the runnng process of centrfugal pump based on numercal and expermental methods, and t satsfes the requrements of the engneerng applcaton. Acknowledgments The authors would lke to thank the Natonal Natural Scence Fund of Chna (No and No ), the Offce of Prorty Academc Program Development of Jangsu Hgher Educaton Insttutons and Jangsu Provncal Project for Innovatve Postgraduates of Chna (Grant No.CXZZ11_0564) for fundng ths research. Specal thanks also goes to Dr. Pan Zhongyong for provdng addtonal detals of the expermental mpeller testng. Nomenclature u Average velocty[m/s] H Head [m] I Turbulence ntensty η Hydraulc effcency[%] Re Reynolds number Vortcty[10 /s] Q Flow rate[m 3 /h] k Turbulent knetc energy[m /s ] u Velocty[m/s] m Standard devaton[%] References [1] Black H F 1969 Journal of Mechancal Engneerng Scence 11() [] Tosho H, Guo Z L and Gordonkrk R 005 Transactons of the ASME, [3] Chen Y, Fe Z T, Ca Y X, et al. 006 Flud Machnery 34(1) 1-5 (n Chnese) [4] Tam L T, Przekwas A J, Muszynska A, et al ASME J. Vbr. Acoust [5] Chlds D W 1991 Journal of Vbraton, Acoustcs, Stress and Relablty n Desgn 113() [6] Wang Y and Zhang X 008 Dranage and Irrgaton Machnery 6(6) 7-30 (n Chnese) 7

9 6th IAHR Symposum on Hydraulc Machnery and Systems IOP Conf. Seres: Earth and Envronmental Scence 15 (01) IOP Publshng do: / /15/7/07017 [7] Wu D Z, Xu B J, Wu P, et al. 011 Journal of Zhejang Unversty(Engneerng Scence) 45(8) (n Chnese) [8] N Y Y 008 Research on the Unsteady Turbulent Smulaton and the Flow-nduced Vbraton n Centrfugal Pump (Ph. D. Thess, Jangsu Unversty: Research Center of Flud Machnery Engneerng and Technology) (n Chnese) [9] Yakhot V and Orszag S A 1986 Renormalzaton Group Analyss of Turbulence J. Sc. Comput, [10] Spezalec G and Thangam S 199 Engneerng Scence 30(10) [11] Asuaje M, Bakr F, Koudrs, et al. 005 Internatonal Journal of Rotatng Machnery [1] Adkns D R and Brennen C E 1988 ASME J. Fluds Eng. 110(1) 0-8 [13] Guan X F 1995 Modern Pump Technology Handbook (Bejng: Astronautcs Press) (n Chnese) 8