Resonance investigation of pump-turbine during startup process

Transcription

1 IOP Conference Serie: Earth and Environmental Science OPEN ACCESS Reonance invetigation of pump-turbine during tartup proce To cite thi article: L Y He et al 2014 IOP Conf. Ser.: Earth Environ. Sci View the article online for update and enhancement. Related content - Characteritic of zirconia nanoparticle prepared by molten alt and microwave ynthei J Grabi, Dz Jankovica, E Sokolova et al. - Microwave aited ynthei of nanocompoite in Zn-Sn-O-Ag ytem and their photocatalytic activity J Grabi, A Letlena, Dz Ramane et al. - Controlled ynthei, characterization and photocatalytic activity of BiPO4 nanotructure with different morphologie Lang-Wei Cheng, Jui-Chien Tai, Tzu-Yun Huang et al. Thi content wa downloaded from IP addre on 04/05/2018 at 01:03

2 Reonance invetigation of pump-turbine during tartup proce L Y He 1, Z W Wang 2, S Kuroawa 3,Y Nakahara 4 1 College of Water Reource & Civil Engineering, China Agricultural Univerity, Beijing, , China 2 Intitute of Fluid Machinery and Fluid Engineering, Department of Thermal Engineering and State Key Laboratory of Hydro cience and Engineering, Tinghua Univerity, Beijing, , China 3 Rotating Machine Technology R&D Department, Power and Indutrial Sytem R&D Center,Tohiba Corporation, 20-1, kanei-cho, Turumi-ku, Yokohama , Japan 4 Hydroelectric Power Engineering Department, Tohiba Corporation, 72-34, Horikawa-cho, Saiwai-ku, Kawaaki , Japan wzw@mail.tinghua.edu.cn Abtract. The caue of reonance of a certain model pump-turbine unit during tartup proce were invetigated in thi article. A three-dimenional full flow path analyi model which contain piral cae, tay vane, guide vane, runner, gap outide the runner crown and band, and draft tube wa contructed. The tranient hydraulic excitation force of full flow path wa analyzed under five condition near the reonance region. Baed on one-way fluid- tructure interaction (FSI) analyi model, the dynamic tre characteritic of the pump-turbine runner wa invetigated. The reult of preure pulation, vibration mode and dynamic tre obtained from imulation were conitent with the tet reult. The tudy indicated that the hydraulic excitation frequency (Z g *f n ) Hz due to rotor-tator interference correponding to the natural frequency of 2ND+4ND runner mode i the main caue of reonance. The relationhip among preure pulation, vibration mode and dynamic tre wa dicued in thi paper. The reult revealed the underlying caue of the reonance phenomenon. 1. Introduction With the improvement of technology of hydraulic turbine, there i a trend to increae the power concentration of the unit. A a conequence, head and fluid velocitie are higher and the hydraulic excitation force on the turbine runner increae. Furthermore, the operation range of hydraulic turbine i widened in order to atify the end-uer demand of larger regulation capacity. For the pump-turbine, preure fluctuation induced by the rotor-tator interaction are the mainly excitation force [1,2]. High excitation force may lead vibration and high tre level which can produce damage by fatigue [3,4]. Therefore, how to predict the natural frequencie and mode hape of the runner a well a the dynamic tre induced by hydraulic excitation force during the deign tage i of paramount importance. Baed on thee characteritic, the invetigation of runner reonance ha an important ignificance to the afety and table operation for pump-turbine. Content from thi work may be ued under the term of the Creative Common Attribution 3.0 licence. Any further ditribution of thi work mut maintain attribution to the author() and the title of the work, journal citation and DOI. Publihed under licence by Ltd 1

3 The natural frequencie and mode hape in water are important parameter for runner deign. Accurately predicting the frequencie and mode hape of runner might be very ueful. By taking effective meaure, it i poible to make the runner avoid reonance, forced vibration or fatigue failure. In the practical operation, becaue the runner i urrounded by water, the vibration of runner tructure will make the urrounding fluid vibrate together. Thu it will produce a certain added ma by water, which will change the modal characteritic of runner. At preent, a lot of reearch achievement of modal behavior of runner in water have been obtained both from tet and imulation. It i how that the natural frequencie and mode hape of runner obtained by experiment which ubmerged the runner in an open water reervoir agree quite well with the finite element imulation reult [5,6,7]. However, conidering the runner i talled in real flow paage in the practical operation, there i a big difference between the channel hape and open reervoir. Furthermore, the olid boundary condition around runner like bottom ring and head cover will change the added ma effect. Epecially when the gap between the olid boundary and runner are very mall and the runner ha enough deformation, the effect i very ignificant [1]. And when it come to pump turbine with high head, the gap between runner and the olid boundary i very mall, o it i neceary to tudy the dynamic characteritic of the runner in real flow path. At preent, a lot of reearcher uing harmonic repone analyi baed on the fluid tructure interaction to analyze the runner dynamic tre caued by rotor-tator interaction. Conidering computing time and torage, the analyi method and object are implified, and o far only ome important excitation frequencie have been choen to analyze intead of all preure pulation frequencie [3,4,8,9]. In thi tudy, reonance phenomenon of the pump turbine wa oberved during the tartup proce. In Tohiba Hydraulic Reearch Laboratory, extenive tudie on thi phenomenon have been carried out by model tet. The reult how that the amplitude of dynamic tre ignificantly increaed at about 88% of rated peed. Thi wa apparently caued by ome reonance of the runner at thi peed. The caue of reonance of the model pump-turbine unit during tartup proce were invetigated by imulation in thi article. The modal characteritic of the runner in the working flow paage were analyzed in detail. Beide, baed on one-way fluid-tructure interaction, tranient dynamic analyi method wa applied in the invetigation of vibration tre caued by hydraulic excitation force due to interference between runner blade and guide vane. 2. Fluid-tructure interaction theory It i well known that the dicretized tructural dynamic equation can be formulated a follow: Where, M i the tructural ma matrix; tiffne matrix; U, the nodal diplacement vector; MU CU KU F (1) C i the tructural damping matrix; F, the applied load vector. K i the tructural Theoretically, to take into account the fluid effect on the ubmerged vibrating tructure, the ytem ha to be treated a a fluid tructure interaction problem. In other word, the tructural dynamic equation ha to be coupled with the fluid equation. The equation for the fluid tructure interaction problem by uing the traditional acoutic method [10], can be written in form of thi [11]. M 0 U C 0 U K K U F f M f M f P 0 C f P 0 K f P 0 In the modal analyi, the damping effect doen t take into account, and the tructure vibrate freely. In thi way, the fluid tructure coupled equation can be implified a follow: (2) M 0 U K K f U 0 M f M f P 0 K f P (3) 2

4 For the M f, it jut conidering the fluid denity and geometry dimenion. However, in the dynamic tre calculation, the fluid added ma effect i calculated. The applied load vector contain the preure, gravity and centrifugal force. The tranient preure load are obtained from three-dimenional full flow path CFD imulation, in which, the flow fluid not only conider the vicou, but alo irrotational. 3. Simulation model The model pump turbine runner ha 6 blade ( Z r ) and a diameter of 404mm. The number of guide vane Z g i 20. The rated head i 492m, and rated peed n r i 4929 rpm. Material denity of runner i 7.75g/cm 3, Elatic modulu i 207GPa, with Poion' ratio 0.3, and the damping ratio of Conidering the operating condition of high head pump turbine are complex and changeable, in order to obtain more accurate hydraulic excitation force characteritic for runner, it i neceary to conider the clearance flow of the gap in the CFD imulation. Accurate analyi of the hydraulic excitation force play an important role to the inner flow characteritic a well a the tructural dynamic repone. Therefore, a three-dimenional full flow path model wa contructed in thi tudy. Except for the main flow channel which include piral cae, tay vain, guide vain, runner, and draft tube, the clearance flow outide the crown, band and eal wa alo taken into account. The calculation model wa hown in Figure 1. The runner part wa elected for modal and dynamic tre analyi, which contain runner tructure and water domain that inide and outide it, a it i howed in Figure 2. However, the hydraulic excitation force applied on runner tructure urface for dynamic tre calculation wa obtained by CFD imulation with full flow paage. Guide vain Clearance Runner-fluid Runner-olid Draft tube Stay vain Spiral cae Figure 1. Calculation model Figure 2. FEM model for dynamic characteritic analyi The reonance point frequency of thi model pump-turbine unit at laboratory i 1446 Hz, in other word, the reonance peed i about 4400 rpm. In order to invetigate the inner flow fluid of the pumpturbine and the dynamic tre characteritic of the runner, and make a comparion to the meaured reult to verify the viability of numerical method, 5 typical working condition were elected for imulation in thi tudy, a lited in Table 1. Table 1. Simulation condition n(rpm) H(m) Q(m 3 /)

5 4. Modal analyi In thi paper, the modal behavior uch a natural frequencie and mode hape of thi model pumpturbine runner wa invetigated. The modal analyi of runner in different condition ha been carried out, like in air, in open water pool and in actual wording flow paage. The typical mode hape of runner both obtained from tet and imulation were compared in Figure3. It can be clearly noticed that the two make a good agreement. Furthermore, it i oberved that the reonant mode hape of the runner wa a combination of 2ND+4ND mode[1]. The natural frequencie of runner in air, open water and work condition were lited in Table.2. By comparing thee reult with meaured value, it i found that the reonance frequency of runner in actual working flow paage wa 1380Hz, which wa very cloe to the tet value of 1446Hz. Therefore, the modal analyi of runner in actual working condition might obtain more accurate reult. Tet reult 2ND 3ND 2ND+4ND (reonant mode) Simulation reult Figure 3. Comparion of runner mode hape between tet and imulation Table 2. Comparion of natural frequencie of runner between tet and imulation. In air (Hz) In water (Hz) Tet Simulation Open water Working flow paage

6 5. Calculation of hydraulic excitation force Unteady imulation reult of different rotating peed condition were hown in Table 3 Conidering the flow field tability and the calculation time, in thi tudy, the total time for calculation of each condition i 20 time of rotation period time. Preure pulation reult data of everal rotation period that after convergence were elected for analyi. Figure 4 preented the preure pulation reult of different monitor point at the rated peed n r (4929 rpm) condition. The above wa the time proce of preure and the below wa the correponding frequency pectra. Here, Monitor P2 i the record point in the outlet of guide vane and near the head cover; Monitor P3 i located in the external gap of the runner crown; And Monitor P4 i the record point in the traight cone ection of draft tube. Table 3. Unteady CFD imulation reult of full flow path of model pump-turbine n(rpm) ΔH(%) ΔQ(%) The reult how that, the dominant frequency of monitor P2 i Z r *f n (f n repreent the rotating frequency), that i the blade paing frequency, mainly affected by the interference of runner blade. While the dominant frequency of monitor P4 i 0.9 f n. A comparion of preure pulation reult between imulation and tet wa made here. The reult of P2 at rated peed condition wa elected. A hown in Figure 5, the red dah line repreent the tet reult, and blue olid line repreent the calculation reult. By comparing the time proce and frequency pectra, it i clearly that both have the ame change trend, and the dominant frequency alo highly conitent. Figure 4. Time proce and frequency pectra of preure pulation of each monitor point Figure 5. Comparion of preure pulation between imulation and tet (P2, n = n r ) 5

7 6. Dynamic tre calculation One-way FSI coupling method wa applied in thi paper. The influence of water around the runner wa conidered in dynamic tre analyi, thu acoutic-tructural coupling calculation method wa introduced to calculate the fluid added ma effect directly. In thi way, it overcome the hortcoming of wating time and reource when uing two-way FSI method, and alo avoid the inaccuracy of without conidering the fluid added ma effect on the tructural repone in the previou reearche. The ditribution contour of tre and diplacement of runner were preented in Figure 6. It i hown that, the maximum deformation wa located at the inlet of runner crown and band between two blade, and the larget tre concentration area appeared at the fillet at the blade root around the inlet edge. Node Node Figure 6. Stre and diplacement ditribution contour of runner The calculation dynamic tre reult of the correponding tet location node of runner crown and band at the reonance peed condition were hown in Figure 7. It i obviouly that the dominant frequency of dynamic tre i Z g *f n, which uggeted that the tator-rotor interaction effect between the guide vane and runner blade wa the main caue of reonance for pump turbine runner. Figure 7. Time proce and frequency pectra of dynamic tre reult (n=0.91n r, reonance condition) The amplitude of dynamic tre reult that uing different calculation model were preented in Figure 8. By comparing to the tet reult, it i confirmed that the reult of the FEM model which conidering the fluid added ma effect wa baically identical with the tet reult. The amplitude of dynamic tre increae ignificantly at about 0.91n r, it mean that, reonance of the runner occur at thi peed. However, the calculation reult without conidering the fluid added ma effect are very different from tet reult. 6

8 Amplitude of dynamic tre (MPa) Rotational peed(n/n r ) CP - Crown Point, BP - Band Point, Sim. - Simulation Figure 8. The comparion of dynamic tre reult between calculation and tet 7. Concluion The caue of reonance of a certain model pump-turbine unit during tartup proce were invetigated in thi article. The following concluion were obtained. 1) The modal analyi method of runner in real working flow paage wa invetigated. The reult of natural frequencie obtained by thi method were more agreeable with the tet reult. The reonance characteritic of the model pump-turbine runner wa accurately analyzed. The actual reonant mode oberved in runner vibration wa a combination of 2ND+4ND mode. 2) The hydraulic excitation force obtained from unteady CFD imulation of full flow path wa more reliable when taken into account the clearance flow outide the runner crown, band and eal. Thi might have a greater influence to the preure fluctuation and runner dynamic tre calculation. 3) Baed on one-way FSI coupling, and conidering the fluid added ma effect, the tranient dynamic tre calculation method can be more accurately to predict the reonance characteritic of runner. The reult of dynamic tre obtained from imulation and tet were quite conitent. The calculated and meaured reult both how that, the amplitude of dynamic tre wa increaed ignificantly near the reonant peed. Acknowledgment The author would like to thank the Tohiba Corporation- Tinghua Univerity cooperate project and National Natural Science Foundation of China (No ) for upporting preent work. Reference [1] Tanaka H 2011 Vibration Behavior and Dynamic Stre of Runner of Very High Head Reverible Pump-turbine. International Journal of Fluid Machinery and Sytem, Vol 4, No 2, pp [2] Sick M, Michler W, Wei T and Keck H 2009 Recent development in the dynamic analyi of water turbine. Proc. of the Intitution of Mechanical Engineer, Part A- Journal of Power and Energy, pp [3] Eguquiza E, Valero C, Huang X X, Jou E, Guardo A and Rodriguez C 2012 Failure invetigation of a large pump-turbine runner. Engineering Failure Analyi, 23, pp

9 [4] Liang Q W, Lai S, Gentner C and Braun O 2012 Efficient runner afety aement during early deign phae and root caue analyi. 26th IAHR Symp. on Hydraulic Machinery and Sytem. Beijing, China [5] Ecaler X, Huumltter J K, Eguquiza E, Farhat M and Avellan F 2010 Modal behavior of a reduced cale pump-turbine impeller. Part I: Experiment. 25th IAHR Symp. on Hydraulic Machinery and Sytem. Timioara, Romania [6] Valero C, Huang X, Eguquiza E, Farhat M and Avellan F 2010 Modal behavior of a reduced cale pump turbine impeller. Part II: Numerical imulation. 25th IAHR Symp. on Hydraulic Machinery and Sytem. Timioara, Romania [7] Lai S, Liang Q W, Henggeler U, Wei T, Ecaler X and Eguquiza E 2009 Dynamic Analyi of Franci Runner - Experiment and Numerical Simulation. International Journal of Fluid Machinery and Sytem, 2(4), pp [8] Seidel U, Hübner B, Löfflad J and Faigle P 2012 Evaluation of RSI-induced tree in Franci runner. 26th IAHR Symp. on Hydraulic Machinery and Sytem. Beijing, China [9] Guillaume R, Deniau J-L, Scolaro D and Colombet C 2012 Influence of the rotor-tator interaction on the dynamic tree of Franci runner. 26th IAHR Symp. on Hydraulic Machinery and Sytem. Beijing, China [10] Kinler L E, Frey A R, Coppen A B and Sander J V 1982 Fundamental of acoutic. (New York: John Wiley and Son) [11] Woyjak D B 1992 Acoutic and fluid tructure interaction, a reviion 5.0. (Houton: Swanon Analyi Sytem Inc) 8