Three-dimensional CFD simulation of solid-liquid two-phase flow in the pumping station forebay with sills

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1 IOP Conference Serie: Earth and Environmental Science Three-dimenional CFD imulation of olid-liquid two-phae flow in the pumping tation forebay with ill To cite thi article: Z H Mi et al 2012 IOP Conf. Ser.: Earth Environ. Sci Related content - Numerical imulation of flow pattern with ill in the front inflow forebay of pumping tation C Luo, L Cheng, C Liu et al. - Numerical invetigation of olid-liquid two phae flow in a non-clogging centrifugal pump at off-deign condition B J Zhao, Z F Huang, H L Chen et al. - Numerical imulation of flow in centrifugal pump under cavitation and ediment condition P C Guo, J L Lu, X B Zheng et al. View the article online for update and enhancement. Thi content wa downloaded from IP addre on 26/02/2019 at 23:50

2 Three-dimenional CFD imulation of olid-liquid two-phae flow in the pumping tation forebay with ill Z H Mi 1, D Q Zhou 1 and Y T Mao 2 1 College of Energy and Electrical, Hohai, Univ. Nanjing, Jiangu, China 2 Hydroelectric Invetigation & Deign Intitute of SPC, Chengdu, Sichuan,China addre: nichola1214m@163.com Abtract. Sill have been ued in the forebay of pumping tation in order to eliminate the circulation and vortex of diffuing flow which impact on pump performance and ediment. In the paper, three-dimenional method i ued to imulate the ill flow in the forebay of pumping tation baed on Eulerian olid-liquid two-phae flow model. Reearch focue on that ill with different ection, dip and poition make important impact to flow pattern and ediment movement. The numerical reult how that the attempt of adopting dicontinuou bottom ill i the mot effective way to eliminate the urface backflow and make the cro-ection velocity ditribution tend to uniform. The velocity at the bottom of the forebay and uction bay and near the pump inlet decreae ignificantly. Sediment accumulation in the forebay and behind the bottom ill are avoided or decreaed. Compared with the literature and experimental reult, it can be confirmed that CFD imulation reult are credible. The further analyi can provide theoretical bai for improving the flow pattern and avoiding ediment depoition in the forebay. 1. Introduction Sediment depoition caued by poor flow of inlet tructure in pumping tation ha a huge negative impact on unit operation and pump tation management[1]. A a modification of flow pattern with the advantage of imple form and convenient contruction, ill ha obviou effect on eliminating vortex and backflow. It come from the fact that ill can damage plane backflow by creating roll wirl of elevation. Studie in the pat mainly focu on mechanim of flow around ill. Feng Xuong analyzed main characteritic parameter and flow pattern behind of ill by tudying on two-dimenion flow through ill applied for forebay of pumping tation[2]. Cheng Li tudied on backflow behind of ill baed on RNG k-ε turbulent model by two-dimenion numerical imulation[3]. However, inlet tructure flow in pumping tation, epecially arrangement with bottom ill, i very complex and how three-dimenional characteritic. Even o, three-dimenional CFD numerical reult of two-phae flow in pumping tation with ill have been rarely reported by now. Therefore, three-dimenional CFD numerical method i ued to imulate flow field and edimentation in pumping tation with ill baed on Eulerian olid-liquid two-phae flow model in the paper. 2. Numerical method The commercial oftware, fluent 6.3, ha been ued to imulate the whole inlet flow field of pump tation. Computational grid conit of almot three billion untructured tetrahedron element built by the Gambit, a a reult of tradeoff between grid enitivity and PC computing capability. Realizable turbulent model i adopted to cloe the Reynold Averaged Navier-Stoke equation. Governing Publihed under licence by Ltd 1

3 equation are dicreted with finite volume method, and econd-order implicit format for time item, econd-order central difference format for diffuion item, econd-order upwind format for convection item, and SIMPLEC method for velocity-preure coupling olution. All kind of boundary condition are et a follow: 1.No-lip boundary condition for the wall, tandard wall function for region near the wall. 2.The ymmetric boundary hypothei for the free urface. 3.Velocity inlet i given to the inlet. 4.Outflow i given to the pump inlet paage outlet where flow i fully developed. In the Euler-Euler approach, different phae are treated mathematically a interpenetrating continua. Since the volume of a phae cannot be occupied by the other phae, the concept of phae volume fraction i introduced. Thee volume fraction are aumed to be continuou function of pace and time and their um i equal to one[4]. The Eluerian model i the mot complex of the multiphae model in FLUENT. It olve a et of n momentum and continuity equation for each phae. Coupling i achieved through the preure and interphae exchange coefficient. The manner in which thi coupling i handle depend upon the type of phae involved, fluid-olid flow are handled differently than fluid-fluid flow. For fluid-olid flow, the phae i alo dependent upon the type of mixture being modeled. The continuity equation of the olid-liquid two-phae flow i decribed a follow: Momentum conervation equation of Liquid-Phae i 1 dll ( l ) ( l vl ) ml l t l dt (1) ( l l l ) ( ll vl vl ) lp l ll g t. l l ( F l F lift, l FVm, l ) Kl ( v vl ) ml vl Momentum conervation equation of Solid-Phae i ( v ) ( v v ) p p t g ( F F lift, F Vm, ) Kl ( vl v). m v l l For Eulerian model, different phae are not interpenetrating and denoted a volume fraction of the phae. In each volume unit, um of all the phae volume fraction i 1[4], volume fraction of and in the inlet and outlet i 0.1 and 0.06 repectively. The denity of and i 2500 kg/m 3 and the vicoity coefficient i kg/m. Water-liquid i choen a primary phae and and a econdary phae in the proce of two-phae imulation. 3. Select characteritic parameter of ill In order to reference the related reearch reult, elect the ame model and flow condition provided by literature[6]. Figure 1 how the whole experimental model arrangement of hydraulic tructure. (2) (3) 2

4 Figure 1. The ketch of the whole experimental model arrangement of hydraulic tructure The height, among variou characteritic parameter of ill, play an important role in improving flow pattern. Height of ill direct effect the length of roller range and flow pattern behind ill. Height of ill i too low, cannot achieve the expected effect; but too high, increaing head lo of dynamic water flow. Rajaratnam uggeted the height i (0.35~0.6)time of water depth[7]; Liu Chao elected the height a (0.4~0.55)time of water depth to imulating[8]. In thi paper, height of ill i 0.45 time of water depth. The common hape of ill i triangle ection, trapezoid ection and rectangular ection. Reearch how that trapezoid ection and rectangular ection have the imilar flow pattern, but rectification effect of triangle ection i poor[9]. Therefore, in thi paper, chooe the bet hape of ill from trapezoid and rectangular ection. Figure 2 to figure 5 are horizontal cro-ection velocity field, plotted with treamline. The numerical imulation reult how that both trapezoid and rectangular ection could create roll wirl in the bottom ill rear. However, roller before ill, can induce backflow which affect flow in uptream, jut caued by trapezoid ection. Therefore, trapezoid i not uitable for uptream ide. Figure 2. Velocity contour and treamline in rectangular ection of ill Figure 3. Velocity contour and treamline in trapezoid ection of ill Figure 4. Velocity contour and Figure 5. Velocity contour and treamline in combination ection of ill treamline in combination ection of ill Seen from figure 6 to figure 9, ediment depoit inevitable near the ill becaue of the low peed area around ill. The comparion reult of numerical imulation how that ill with rectangular form ha lighter ediment depoition. 3

5 Figure 6. Contour of and volume fraction in rectangular ection of ill Figure 7. Contour of and volume fraction in trapezoid ection of ill Figure 8. Contour of and volume Figure 9. Contour of and volume fraction in combination ection of ill fraction in combination ection of ill According to numerical reult of experimental model, ill with rectangular form i the optimal cheme. 4. Water retaining ill application in forebay of pumping tation In the tudy, five haft tubular pump unit were intalled and deign flow of ingle pump wa 34m/. The length of the pump tation include approach channel, forebay and intake ump i 690m. Under the deign condition, total flow Q of five pump i equal to m 3 / and water depth i 1.88 m. Figure 10 how the whole preliminary arrangement of hydraulic tructure. Figure 10. The ketch of the whole preliminary arrangement of hydraulic tructure 4.1. Eulerian two-phae flow numerical reult of preliminary cheme In order to analyze the numerical reult, horizontal cro-ection i intercepted 0.1m from the bottom floor, in which elevation i -2.5m, and the free water urface. In the paper, time tep i et a and Max iteration per time tep i 40. The numerical reult after 30 econd are a follow:. Figure 11 and figure 12 i horizontal cro-ection velocity field, plotted with treamline. Figure 12 indicate that preliminary layout cheme of hydraulic tructure make main flow run near the right ide of approach channel, which caue vortex occurrence on the left ide of forebay. Comparing 4

6 figure 11 with figure 12, it i hown that vortex in the left ide of forebay i a deep one which extend from urface to bottom, but vortex occurrence on the left of approach canal i a hallow one which jut appear on the urface. Figure 13 how that due to the luice gate i cloed, ill of ediment retaining induce mot and to depoit in downtream low velocity region of river. However, a few and till enter approach channel and depoit in the low velocity region on the left ide of forebay. Seen from figure 11 to figure 13, the vortex area ha no ignificant ediment becaue it vortex tructure i deep with high velocity of flow at the bottom of pump tation. Sediment mainly depoit in the left ide of forebay, which agree with the ditribution characteritic of low velocity region diplayed in the figure 5 and figure 6. Figure 11. Velocity contour and treamline in H=-2.4m horizontal ection for the preliminary cheme Figure 12. Velocity contour and treamline in H=1.88m horizontal ection for the preliminary cheme Figure 13. Contour of and volume fraction in H=- 2.4m horizontal ection for thepreliminary cheme According to numerical reult of preliminary cheme, ome meaure hould be taken to improve hydraulic performance and decreae ediment depoition Eulerian two-phae flow numerical reult of improved cheme According to the fact that the length of forebay i relatively hort and diffuion angle i too large, dicontinuou bottom ill which have clearance between ill and lateral wall i et in the tranition of forebay in order to eliminate the vortex and decreae ediment on the left ide of forebay. Height of ill i 1.971m which i 0.45 time of water depth, and the ill with rectangular form i introduced into thi paper. The whole arrangement of the improved cheme i hown in the figure 14. 5

7 Figure 14. Three dimenional ketch of the whole improved arrangement of hydraulic tructure The elected ection for analyi are the ame a the preliminary cheme and numerical reult are a follow: Seen from figure 15 and figure 16, it can be found that under the dicontinuou water retaining ill, vortex region on the left ide of forebay ha been eliminated, and flow become more uniform than the preliminary cheme. Comparing figure 9 with figure 5, it i hown that the flow pattern in the forebay i optimized ignificantly and vortex i eliminated. Comparing figure 10 with figure 6, it can be een that the bia flow in the approach channel i not o obviouly, and low-peed area become maller than before. Figure 15. Velocity contour and treamline in H=-2.4m horizontal ection for the improved cheme Figure 16. Velocity contour and treamline in H=1.88m horizontal ection for the improved cheme Figure 17 indicate that mot and have been blocked by ediment retaining ill and depoit in the downtream river. Sedimentation region in the left ide of forebay become very mall becaue of forebay flow pattern improvement. Sediment depoition behind the bottom ill agree with the ditribution characteritic of low velocity region diplayed in the figure 2. 6

8 Figure 17. Contour of and volume fraction in H=-2.4m horizontal ection for the improved cheme 5. Concluion In the paper, the flow feature and edimentation of the whole pump tation inlet field have been analyzed by the CFD method. From the numerical reult, ome concluion can be drawn a follow: (1) Eulerian olid-liquid two-phae flow imulation i an effective method to entirely meticulou analyi the complex flow pattern in forebay of pumping tation and revealed the correlativity between flow field and ediment depoition. (2) Dicontinuou water retaining ill can improve flow pattern by increaing velocity of ide wall, decreae edimentation in the forebay ignificantly by eliminating low velocity region. (3) The reult of thi tudy need to be further verified by actual operation of pumping tation. Nomenclature c F l F lift, q coefficient of ediment an external body force a lift force F vm, q g H K k l m l p Q v l v a virtual ma force acceleration due to gravity the horizontal cro-ection height Kl Momentum exchange coefficient between fluid or olid phae l and olid phae turbulent kinematic energy Ma tranfer from Solid-Phae to Liquid-Phae the olid preure flow rate (m 3 /) Velocity of Liquid-Phae Velocity of Solid-Phae 7

9 l l l turbulent diipation rate Liquid-Phae volume fraction Solid-Phae volume fraction Shear tre tenor of Liquid-Phae Shear tre tenor of Solid-Phae Gradient Phyical denity of liquid phyical denity of olid Acknowledgement The upport of College of Energy and Electrical, Hohai Univerity, China i gratefully acknowledged. Thi reearch project i ponored by Natural Science Foundation of China (No ) Reference [1] Cong R Y, Chen Y L and Feng J G 2005 J. China Rural Water and Hydropower [2] Feng X S 1998 J. Jiangu Water Reource (1) 31~33 [3] Cheng L, Liu C, Zhou J R, Tang F P and Yuan J B 2001 J. Drainage and Irrigation Machinery 19(1) [4] FLUNENT INC. Fluent Manual M. Fluent Inc. Technical Reference [5] Cao Z X, Wei L Y and Xie J H 1995 Journal of Hydraulic Engineering [6] Cheng L, Liu C, Zhou J R and Tang F P 2001 Journal of Hohai Univerity 29(4) [7] Rejaratnam N and Nwachokw B A 1983 Joun of Hydraulic Engineering ASCE [8] Liu C 2009 The PIV experiment on the forebay of pumping tation with the ide intake channel Ph.D Thei (Yangzhou:YangZhou Univerity) [9] Cheng L, Liu C, Zhou J R and Tang F P 2005 J. Tranaction of the Chinee Society of Agricultural Machinery [10] Contantinecu G, Patel V C 1998 Journal of Hydraulic Engineering ASCE 124(2) [11] Jian Y, McCorquodate J A 1998 Journal of Hydraulic Engineering ASCE 124(7) [12] Matahel A,Tatuaki N 2001 Journal of HydraulicEngineering ASCE 127(10) [13] Liu X Y,Gao C C,Shi L W and Liu W 2010 Journal of Drainage and Irrigation Machinery Engineering 28(3) [14] Barkdoll B D 1997 Sediment Control at Lateral Diverion Ph.D Thei (Lowa: Univerity of lowa) [15] Wei H P and Liu C 1999 Journal of Tongji Univerity (27)