선회류에 의한 흡출관의 내부유동 해석

전현태(H. T. Jeon),남상현(S. H. Nam),최영도(Y. D. Choi),김유택(Y. T. Kim),이영호(Y. H. Lee) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-

Small hydropower attracts attention because of its clean, renewable and abundant energy resources to develop. However, suitable draft-tube type is not determined yet because of its complicated internal flow and unstable turbine performance at the partial flow rate by the influence of the draft tube configuration. Therefore, it is necessary to study the influence of draft tube shape. The purpose of this study is to investigate the influence of the draft tube shape to its internal flow using CFD analysis. The results using two different computational models (draft tube without runner and draft tube with runner) are compared. The result which is computed without runner show that large secondary flow occurs at the curve area of the draft tube and the secondary flow goes out to the outlet of the draft tube. Another result which is computed with runner show that internal flow has complex flow in the whole flow field of the draft tube.

Optimal design of J-groove shape on the suppression of unsteady flow in the Francis turbine draft tube

Zhenmu Chen,백석흠,조현규,최영도 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.5

The flow in the draft tube of a Francis turbine is highly complex and unstable when the turbine operates far from its design point. To extend the Francis turbine operation range to meet the variable energy demand, a J-groove technology is introduced on the turbine draft tube wall to stabilize the unsteady flow in the draft tube. However, J-groove contributes to energy losses in the draft tube. In this study, the Jgroove shape optimization process is proposed based on steady flow analysis using the response surface method. The energy loss and swirl intensity in the draft tube are selected as objectives for the optimization design. The flow characteristics in the draft tube without J-groove and with initial J-groove and optimized J-groove shape are compared. Results show that the swirl intensity in the draft tube with the optimized J-groove is suppressed effectively with the low energy loss in the draft tube. Moreover, the pressure fluctuation in the draft tube with the optimized J-groove is mitigated significantly to stabilize the Francis turbine operation under the off-design point condition.

Effect of J-Groove design parameter on suppression of swirl flow in draft tube of francis hydro turbine

Ujjwal Shrestha,최영도 한국마린엔지니어링학회 2019 한국마린엔지니어링학회지 Vol.43 No.8

Hydropower is the most versatile source of electricity. Francis hydro turbine is a major turbine in contribution to the hydropower sector. Francis hydro turbine operates in a wide operating range from deep partial load to full load condition. While operating in partial load condition, Francis turbine suffers from the unwanted swirl flow. Swirl flow will distort the flow in the draft tube to cause unsteady pressure fluctuation and vortex rope. This pressure fluctuation and vortex rope are the main reason for the vortex-induced vibration in the draft tube. The vibration is an unwanted phenomenon in the hydro turbine and cause of structured failure. Due to this reason, many techniques have implemented in the draft tube for suppression of swirl flow and vortex-induce vibration. J-groove is one of the methods for the suppression of swirl flow in the draft tube of Francis hydro turbine. J-Groove is the simple groove that mounted on the draft tube wall. The major design criteria for J-Groove are the length, depth, and number. The numerical analysis was performed to determine the effect of the J-Groove in the suppression of swirl flow in the draft tube. The performance results from the experiment and CFD analysis have compared for validation of the numerical method. Furthermore, the influence of the design parameter of the J-Groove on the suppression of swirl flow and loss in the draft tube has been studied. Moreover, the proper design criteria for the J-Groove has been set for the suppression of swirl flow in the draft tube.

Quantitative and qualitative analysis of the flow field development through T99 draft tube caused by optimized inlet velocity profiles

Galvan, Sergio,Reggio, Marcelo,Guibault, Francois,Solorio, Gildardo Korean Society for Fluid machinery 2015 International journal of fluid machinery and syste Vol.8 No.4

The effect of the inlet swirling flow in a hydraulic turbine draft tube is a very complex phenomenon, which has been extensively investigated both theoretically and experimentally. In fact, the finding of the optimal flow distribution at the draft tube inlet in order to get the best performance has remained a challenge. Thus, attempting to answer this question, it was assumed that through an automatic optimization process a Genetic Algorithm would be able to manage a parameterized inlet velocity profile in order to achieve the best flow field for a particular draft tube. As a result of the optimization process, it was possible to obtain different draft-tube flow structures generated by the automatic manipulation of parameterized inlet velocity profiles. Thus, this work develops a qualitative and quantitative analysis of these new draft tube flow field structures provoked by the redesigned inlet velocity profiles. The comparisons among the different flow fields obtained clearly illustrate the importance of the flow uniformity at the end of the conduit. Another important aspect has been the elimination of the re-circulating flow area which used to promote an adverse pressure gradient in the cone, deteriorating the pressure recovery effect. Thanks to the evolutionary optimization strategy, it has been possible to demonstrate that the optimized inlet velocity profile can suppress or mitigate, at least numerically, the undesirable draft tube flow characteristics. Finally, since there is only a single swirl number for which the objective function has been minimized, the energy loss factor might be slightly affected by the flow rate if the same relation of the axial-tangential velocity components is maintained, which makes it possible to scale the inlet velocity field to different operating points.

Quantitative and qualitative analysis of the flow field development through T99 draft tube caused by optimized inlet velocity profiles.

Sergio Galván,Marcelo Reggio,François Guibault,Gildardo Solorio 한국유체기계학회 2015 International journal of fluid machinery and syste Vol.8 No.4

The effect of the inlet swirling flow in a hydraulic turbine draft tube is a very complex phenomenon, which has been extensively investigated both theoretically and experimentally. In fact, the finding of the optimal flow distribution at the draft tube inlet in order to get the best performance has remained a challenge. Thus, attempting to answer this question, it was assumed that through an automatic optimization process a Genetic Algorithm would be able to manage a parameterized inlet velocity profile in order to achieve the best flow field for a particular draft tube. As a result of the optimization process, it was possible to obtain different draft-tube flow structures generated by the automatic manipulation of parameterized inlet velocity profiles. Thus, this work develops a qualitative and quantitative analysis of these new draft tube flow field structures provoked by the redesigned inlet velocity profiles. The comparisons among the different flow fields obtained clearly illustrate the importance of the flow uniformity at the end of the conduit. Another important aspect has been the elimination of the re-circulating flow area which used to promote an adverse pressure gradient in the cone, deteriorating the pressure recovery effect. Thanks to the evolutionary optimization strategy, it has been possible to demonstrate that the optimized inlet velocity profile can suppress or mitigate, at least numerically, the undesirable draft tube flow characteristics. Finally, since there is only a single swirl number for which the objective function has been minimized, the energy loss factor might be slightly affected by the flow rate if the same relation of the axial-tangential velocity components is maintained, which makes it possible to scale the inlet velocity field to different operating points.

An Outlook on the Draft-Tube-Surge Study

Michihiro Nishi,Shuhong Liu 한국유체기계학회 2013 International journal of fluid machinery and syste Vol.6 No.1

If large pressure fluctuation is observed in the draft tube of a Francis turbine at part-load operation, we have generally called it draft-tube-surge. As occurrence of this phenomenon seriously affects the limit of turbine operating range, extensive studies on the surge have been made since proposal of surge-frequency criterion given by Rheingans. According to the literature survey of related topics in recent IAHR symposiums on hydraulic machinery and systems, in which state-of-the-art contributions were mainly presented, a certain review of them may be desirable for an outlook on the future studies in this research field. Thus, in this review paper, the authors' previous attempts for the last three decades to challenge the following topics: a rational method for component test of a draft tube, nature of spiral vortex rope and its behavior in a draft tube and cavitation characteristics of pressure fluctuations, are introduced together with other related contributions, expecting that more useful and significant studies will be accomplished in the future.

An Outlook on the Draft-Tube-Surge Study

Nishi, Michihiro,Liu, Shuhong Korean Society for Fluid machinery 2013 International journal of fluid machinery and syste Vol.6 No.1

If large pressure fluctuation is observed in the draft tube of a Francis turbine at part-load operation, we have generally called it draft-tube-surge. As occurrence of this phenomenon seriously affects the limit of turbine operating range, extensive studies on the surge have been made since proposal of surge-frequency criterion given by Rheingans. According to the literature survey of related topics in recent IAHR symposiums on hydraulic machinery and systems, in which state-of-the-art contributions were mainly presented, a certain review of them may be desirable for an outlook on the future studies in this research field. Thus, in this review paper, the authors' previous attempts for the last three decades to challenge the following topics: a rational method for component test of a draft tube, nature of spiral vortex rope and its behavior in a draft tube and cavitation characteristics of pressure fluctuations, are introduced together with other related contributions, expecting that more useful and significant studies will be accomplished in the future.

CFD에 의한 흡출관의 내부유동 해석

전현태(Hyun-Tae Jeon),남상현(Sang-Hyun Nam),최영도(Young-Do Choi),김유택(You-Taek Kim),이영호(Young-Ho LEE) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10

Small hydropower attracts attention because of its clean, renewable and abundant energy resources to develop. However, suitable draft-tube type is not determined yet because of its complicated internal flow and unstable turbine performance at the partial flow rate by the influence of the draft tube. Therefore, it is necessary to study the influence of draft tube shape. The purpose of this study is to investigate the influence of the draft tube shape to its internal flow using CFD analysis. The results show that large secondary flow occurs at the curve area of the draft tube and the secondary flow goes out to the outlet of the draft tube in the case of no-prerotation condition of the inlet flow.

A Novel Guide Vane System Design to Mitigate Rotating Vortex Rope in High Head Francis Model Turbine

Jesline Joy,Mehrdad Raisee,Michel J. Cervantes 한국유체기계학회 2022 International journal of fluid machinery and syste Vol.15 No.2

Guide vanes are a mechanical system used to direct flow in the desired direction. At lower operating conditions, implementing a guide vane system in the draft tube of a hydro-turbine can decrease the excess swirl in the flow and, thus, reduce pressure fluctuations. The present study discusses a numerical methodology to design an effective guide vane system in the draft tube of a high head Francis model turbine. The numerical method is computationally efficient and thus, saves excess computational time and data storage required for parametric analysis of the guide vane system. The aim is to mitigate the ‘rotating’ vortex rope with minimum additional losses in the turbine. The factors considered for the guide vane system design are a) number of guide vanes, b) chord length, c) span, d) inlet-outlet angles of the guide vanes, and e) their position in the draft tube. The parametric study comprises a) ideal guide vane design and b) realistic guide vane design study. The ideal guide vane design study was with the standalone draft tube domain. The realistic guide vane design study used the passage domains of the distributor, runner, and complete draft tube. From the ideal guide vane design study, a guide vane system with two or three guide vanes of chord 86% of runner radius and leading-edge span of 30% of runner radius effectively mitigates the rotating vortex rope. The system with three guide vanes is the most efficient when placed at some distance below the runner exit with mitigation above 95%

Numerical Investigation of Pressure Fluctuation Reducing in Draft Tube of Francis Turbines

W F Li,J J Feng,H Wu,J L Lu,W L Liao,X Q Luo 한국유체기계학회 2015 International journal of fluid machinery and syste Vol.8 No.3

For a prototype turbine operating under part load conditions, the turbine output is fluctuating strongly, leading to the power station incapable of connecting to the grid. The field test of the prototype turbine shows that the main reason is the resonance between the draft tube vortex frequency and the generator natural vibration frequency. In order to reduce the fluctuation of power output, different measures including the air admission, water admission and adding flow deflectors in the draft tube are put forward. CFD method is adopted to simulate the three-dimensional unsteady flow in the Francis turbine, to calculate pressure fluctuations in draft tube under three schemes and to compare with the field test result of the prototype turbine. Calculation results show that all the three measures can reduce the pressure pulsation amplitude in the draft tube. The method of water supply and adding flow deflector both can effectively change the frequency and avoid resonance, thus solving the output fluctuation problem. However, the method of air admission could not change the pressure fluctuation frequency.