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.

Active Control of the Vortex Induced Pressure Fluctuations in a Hydro Turbine Model via Axial and Radial Jets at the Crown Tip

Ivan Litvinov,Daniil Suslov,Mikhail Tsoy,Evgeny Gorelikov,Sergey Shtork,Sergey Alekseenko,Kilian Oberleithner 한국유체기계학회 2023 International journal of fluid machinery and syste Vol.16 No.4

This paper presents an active method to control the pressure fluctuations induced by the rotating vortex rope (RVR) in a Francis hydro turbine model under part load conditions. The control method is based on the injection of axial or radial jets through a stagnant crown attached to the hydro turbine runner. A wide range of injection strategies are com-pared, and the effectiveness of suppressing pressure fluctuations is analyzed in terms of the spatial distribution of the jets and the flow rate required to suppress the oscillations. The experiments are performed on a fully automated aerody-namic test rig. The pressure fluctuations are quantified using data from the four acoustic sensors placed at a cross sec-tion in the cone of the hydro turbine draft tube. The best suppression of pressure fluctuations is achieved with a radial actuator. At a control flow rate of 2% of the main flow, the pressure fluctuations at the vortex rope frequency are re-duced by 80% in terms of PSD compared to the baseline case without control. The presented control method will be useful for extending the operating range of Francis hydro turbines.

A Study on the Effect of Port Area of Blade on the Performance of Francis Hydro Turbine

천쩐무,최영도 한국유체기계학회 2016 한국유체기계학회 논문집 Vol.19 No.1

As a key component of a Francis turbine facility, the runner performance plays a vital role in the performance of the turbine. It is effective and successful to design a Francis turbine runner blade with good performance by one dimensional hydraulic design method. On the basis of one dimensional hydraulic analysis, there are a lot of parameters of the internal flow passage shapes determined by experience. Among those parameters, the effect of port area of blade on the performance of a Francis turbine is investigated in this study. A given Francis turbine model was selected for investigating the port area of blade on the performance. The result shows that the effect of port area of runner blade on the outflow angle from runner passage on the performance is quite significant. A correct exit flow angle reduces the energy loss at draft tube, which has the best efficiency of the turbine model.

Suppression of flow instabilities in the stay vane passage of the Francis hydro turbine model by design optimization

Ujjwal Shrestha,Young-Do Choi 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.1

The oscillating flow is a problem occurring in the stay vane passage of hydro turbines. The improper shape of the stay vane causes wake formation and sheds large eddies in the trailing edge of the stay vane. The wake at the trailing edge of the stay vane produces pressure fluctuation in the stay vane passage, which leads to noise and vibration during the turbine operation. Therefore, the improper shape of the stay vane may cause flow oscillation in the stay vane passage. Thus, a proper shape design of the stay vane considering the oscillating flow is necessary to mitigate the flow instability. Consequently, experiment and CFD analyses showed that the initial stay vane (ISV) shape causes recirculation and pressure fluctuation. An optimum design methodology is adopted to improve the flow behavior around the stay vane. Optimization of the stay vane is also conducted by using two objective functions (turbine efficiency and flow uniformity) and 12 design variables. The optimal stay vane (OSV) shape is attained by a multi-objective genetic algorithm. Finally, the flow behavior in the stay vane passage with ISV and OSV is compared by experiment and CFD analyses. Thus, the flow instabilities are mitigated with OSV. The installation of OSV improved the flow angle distribution, secondary flow, and pressure fluctuation in the Francis hydro turbine.

Suppression of flow instability in the Francis hydro turbine draft tube by J-groove shape optimization at a partial flow rate

Ujjwal Shrestha,최영도 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.6

Flow instability and pressure fluctuation are common problems in hydro turbines, especially in partial flow conditions. When Francis hydro turbine operates at partial flow rate, swirl flow occurs at the runner outlet, which is the cause of pressure pulsations, vortex core, noise and vibration in the draft tube. Among various methods, J-groove was selected and mounted in the draft tube to suppress the swirl flow. The study focuses on the Jgroove incorporation in a draft tube from the design process to optimization. The optimization focused on the suppression of swirl flow with minimum efficiency drop. The turbine efficiency and swirl number were selected for the optimization, which encounters global and local effects of J-groove installation on the Francis hydro turbine. J-groove shape optimization was performed by response surface methodology (RSM) and multi-objective genetic algorithm (MOGA). The flow behavior in the draft tube was compared without and with the initial and optimal J-groove shapes. The optimal J-groove shape is more effective in swirl flow suppression than the initial J-groove shape. Additionally, the installation of the J-groove did not hinder turbine performance. Therefore, the optimal J-groove shape improved flow behavior in the draft tube at the partial flow rate.

Correlation of the Sediment Properties and Erosion in Francis Hydro Turbine Runner

Ujjwal Shrestha,Zhenmu Chen,Young Do Choi 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.2

Sediment erosion is the main problem for the hydropower situated in South Asia and South America. Due to sediment erosion, hydropower in those areas cannot operate in their full potential. Sediment erosion is a significant problem in turbomachinery and associated with degradation of turbine performance. The sediment erosion removes the turbine material from its surface. It can cause fracture of the turbine, which leads to an economic loss. In this paper, the sediment properties and its influence on erosion have discussed. Sediment properties like shape, size, and concentration have a direct influence on erosion. The numerical analysis was conducted to visualize the erosion in Francis hydro turbine. The most vulnerable area for the sediment erosion in Francis hydro turbine has predicted. The precise prediction of the sediment erosion in the turbine is the difficult task due to the synergetic effect of sediment parameters (shape, size, concentration, hardness, velocity). The accurate and precise indication of the sediment erosion required both experimental and computational analysis. In this study, solid-fluid computational analysis has done to identify the susceptible area on runner blade and influence of sediment parameters on erosion.

프란시스 수차 모델의 블레이드 내 와류 특성에 대한 수치해석적 분석

김승준,최영석,조용,최종웅,김진혁 한국유체기계학회 2019 한국유체기계학회 논문집 Vol.22 No.2

In this study, a numerical analysis of the inter-blade vortex characteristics of a Francis hydro turbine model was performed with various flow rate conditions in the operating range. The model turbine demonstrated notably different internal flow characteristics for different operating conditions. Particularly, an inter-blade vortex between the runner blade passages was observed at lower flow rate conditions. An inter-blade vortex can cause reduction in performance, and vibration and instability in the operation of a turbine system. Therefore, understanding inter-blade vortex characteristics is important for the safe and stable operation of turbines. To investigate internal flow and unsteady pressure characteristics, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes calculations using a shear stress transport turbulence model were performed with two-phase flow analysis. Inter-blade vortices were captured at the leading and trailing edges of the near runner hub between blade passages. This vortex region exhibited flow separation and lower velocity and contributed to decreased hydraulic performance and higher unsteady pressure characteristics.

Shape Design Optimization of Draft Tube with J-groove of a Francis Hydro Turbine Model

Ujjwal Shrestha(쉬레스트 우즈왈),Young-Do Choi(최영도) 한국신재생에너지학회 2021 한국신재생에너지학회 학술대회논문집 Vol.2021 No.7

Flow instability and pressure fluctuation are the main problems that occurred in the Francis hydro turbine draft tube. The swirling flow and vortex core occurred in the runner outlet at partial load conditions. Among various techniques, J-groove was introduced in the draft tube to stabilize the swirl flow from the runner outlet because the J-groove design is simple and creates a reverse flow mechanism through grooves. In the study, J-groove was installed in the draft tube and optimized the J-groove shape at a partial flow rate for the swirl flow suppression without depleting turbine efficiency. Hence, swirl number and turbine efficiency were selected for the J-groove shape optimization. The optimal J-groove was obtained from a multi-objective genetic algorithm (MOGA). The flow behavior in the draft tube without with initial and optimal J-groove was compared. It concluded that the optimal J-groove shape improved the flow characteristics in the draft tube of Francis hydro turbine at partial load conditions.

Effect of blade thickness on the hydraulic performance of a Francis hydro turbine model

Kim, Seung-Jun,Choi, Young-Seok,Cho, Yong,Choi, Jong-Woong,Kim, Jin-Hyuk Elsevier 2019 RENEWABLE ENERGY Vol.134 No.-

<P><B>Abstract</B></P> <P>Francis turbines are the most commonly used turbines for hydroelectric power generation. Preliminary studies to verify turbine designs are often performed with small-scale models; however, when the runner blade of a full-size turbine is geometrically scaled down to prepare a model for evaluating the design variables and performance characteristics, the blades become very thin and difficult to manufacture. Hence, the blockage effect of the runner blade should be considered to find a suitable blade thickness that satisfies the required hydraulic performance. Furthermore, a clear understanding of the blockage ratio at the highest efficiency point and off-design condition is required to investigate different blade thicknesses and performance characteristics. Here, the blockage effect of the runner blade on the hydraulic performance and internal flow characteristics of a 300-class Francis hydro turbine was investigated. Three-dimensional Reynolds-averaged Navier–Stokes calculations were performed with a shear stress transport turbulence model to analyze the internal flow characteristics near the runner blade and compare the blockage effect with various blade thicknesses on major performance parameters such as the hydraulic efficiency. Flow analyses for the off-design conditions were also performed with various blade thicknesses. The obtained results indicated that the power and efficiency gradually decreased with increasing blockage ratio. The runner head loss increased due to the mismatches between the flow angle and blade angle with changing the inlet velocity triangle components according to blockage ratio. Especially the efficiency of approximate 3.4% decreased as the blockage ratio increased with 12.5%, compared to the reference model. It was verified that the blockage effect significantly affects the design of Francis turbine models.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of blade thickness on the performance of a Francis turbine was presented. </LI> <LI> The definition of the blockage ratio for runner was applied with numerical analysis. </LI> <LI> The blockage effects were investigated at best efficiency and off-design conditions. </LI> <LI> The power and efficiency gradually decreased as the blockage ratio increased. </LI> <LI> The efficiency of about 3.4% decreased as the blockage ratio increased with 12.5%. </LI> </UL> </P>

Runner Design and Internal Flow Characteristics Analysis for an Ns=200 Francis Hydro Turbine Model

Yeong-Cheol Hwang,Zhenmu Chen,Young-Do Choi,Young-Ho Lee 한국마린엔지니어링학회 2016 한국마린엔지니어링학회지 Vol.40 No.8