Analysis of the internal flow behavior on S-shaped region of a Francis pump turbine on turbine mode

2016 ◽  
Vol 33 (2) ◽  
Author(s):  
Yexiang Xiao ◽  
Wei Zhu ◽  
Zhengwei Wang ◽  
jin zhang ◽  
Chongji Zeng ◽  
...  
Keyword(s):  
Design Methodology ◽  
Flow Characteristic ◽  
Stokes Equations ◽  
Flow Behavior ◽  
Internal Flow ◽  
Optimal Operation ◽  
Operating Conditions ◽  
Unit Discharge ◽  
Pump Turbine ◽  
Runner Blade

Purpose Numerically analyzed the flow characteristic and explored the hydrodynamic mechanism of the S-shaped region formation of a Francis pump-turbine. Design/methodology/approach Three-dimensional steady and unsteady simulations were performed for a number of operating conditions at the optimal guide vanes opening. The steady Reynolds averaged Navier-Stokes equations with the SST turbulence model were solved to model the internal flow within the entire flow passage. The predicted discharge-speed curve agrees well with the model test at generating mode. This paper compared the hydrodynamic characteristics of for off-design cases in S-shaped region with the optimal operating case, and more analysis focuses particularly on very low positive and negative discharge cases with the same unit speed. Findings At runaway case towards smaller discharge, the relative circumferential velocity becomes stronger in the vaneless, which generates the “water ring” and blocks the flow between guide vane and runner. The runner inlet attack angle becomes larger, and the runner blade passages nearly filled with flow separation and vortexes. The deterioration of runner blade flow leads to the dramatic decrease of runner torque, which tends to reduce the runner rotation speed. In this situation, the internal flow can’t maintain the larger rotating speed at very low positive discharge cases, so the unit discharge-speed curves bend to S-shaped near runaway case. Originality/value The analysis method of four off-design cases on S-shaped region with the comparison of optimal operation case and the calculated attack angles are adopted to explore the mechanism of S characteristic. The flow characteristic and quantitative analysis all explain the bending of the unit discharge-speed curves.

Hydrodynamic mechanism analysis of the pump hump district for a pump-turbine

2016 ◽  
Vol 33 (3) ◽  
Author(s):  
Yexiang Xiao ◽  
Yangyang Yao ◽  
Zhengwei Wang ◽  
jin zhang ◽  
Yongyao Luo ◽  
...  
Keyword(s):  
Design Methodology ◽  
Flow Characteristic ◽  
Internal Flow ◽  
Hydraulic Loss ◽  
Pump Mode ◽  
Pump Turbine ◽  
Flow Passage ◽  
Hydrodynamic Mechanism ◽  
Flow Components ◽  
Dominant Frequencies

Purpose Numerically analyzed the flow characteristic and explored the hydrodynamic mechanism of the pump mode hump district formation of a Francis pump-turbine. Design/methodology/approach Numerical simulations were conducted of the entire pump-turbine flow passage under different discharge conditions by adopting the SST-CC turbulence model. The internal flow at hump district has been explained in detail combined with the model test in this paper. The unsteady flow and pressure fluctuation characteristics are analysed under five different discharge conditions in the hump and nearby region. The reason of the hump district formation is explored combined with the flow components hydraulic loss. Findings The large hydraulic loss, high relative peak-to-peak amplitudes and low dominant frequencies are on account of the disorganized internal flow condition. The formation of the hump district is concerned with the large hydraulic loss inside the draft tube, runner and guide vanes as there occurs secondary flow, backflow even vortex in the hump district. In addition, the low dominant frequencies at recording points inside the flow passage are always accompanied with the change of flow patterns and the spreading of the pressure fluctuations. Originality/value The analysis method of each flow components hydraulic loss combined with internal flow structure is adopted to explore the mechanism of pump mode hump characteristic. The flow characteristic and pressure pulse characteristics all correspond to the flow components hydraulic loss.

Numerical Analysis of the Effect of Misaligned Guide Vanes on Improving S-Shaped Characteristics for a Pump-Turbine

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Xiao Yexiang ◽  
Zhu Wei ◽  
Wang Zhengwei ◽  
Zhang Jin ◽  
Ahn Soo-Hwang ◽  
...  
Keyword(s):  
Numerical Analysis ◽  
High Speed ◽  
Flow Behavior ◽  
Internal Flow ◽  
Operating Conditions ◽  
Guide Vanes ◽  
Electrical Grid ◽  
Runner Blade ◽  
Discharge Rates ◽  
Unit Speed

The S-shaped characteristic curves in pump-turbines complicate synchronization with the electrical grid and affect system safety. Misaligned guide vanes (MGVs) are one of the most effective solutions to avoid S-shaped characteristics. The internal flow mechanism with the MGV for improving S-shaped characteristics was studied by numerical analysis. Six operating conditions were modeled in the S-shaped region. Four guide vanes were arranged as the MGVs to qualitatively and quantitatively analyze the flow behavior. The internal flow was quite complex at the four operating points without the MGV; here, the attack angle and the flow behavior had no obvious difference at each vane. For the similar conditions with MGVs, attack angles and internal flow fields varied clearly at each vane, especially in the vaneless region and in the runner blade passages. For the same discharge rates, total openings, and rotating speeds, the internal flows were quite different between with and without the MGVs. The MGVs disrupt the high-speed circumferential water ring (appreciably faster compared to the main flow) in the vaneless region and maintain operation with higher unit speeds. Consequently, the unit speed is larger at the same unit discharge in the S-shaped region. Therefore, the MGV method can reduce S-shaped characteristics.

Measurement of Unsteady Flow in Pump-Turbine for Hydropower Using PIV Method

2009 ◽  
Author(s):  
Nobuhiko Fukuda ◽  
Satoshi Someya ◽  
Koji Okamoto
Keyword(s):  
Rotational Speed ◽  
Velocity Measurement ◽  
Numerical Procedure ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
High Time ◽  
Pump Turbine ◽  
Guide Vanes ◽  
Runner Blade ◽  
Wide Range

It is thought that the pressure fluctuation can occur due to the interaction between flow through guide vanes and flow into runner blades, resulting in a vibration of turbine and a blade cracking, in a hydraulic turbine operated in a wide range for flexible power demand. High accurate velocity measurement with high time/spatial resolution can help to clarify the mechanism of the interaction and to provide good experimental data for the validation of numerical procedure. So the aim of present study is to estimate the unstable velocity field quantitatively in the area between guide vanes and runner blades, using high time-resolved particle image velocimetry (PIV). Two types of velocity measurements were carried out, i.e., phase-locked measurement and high time sequential velocity measurement, in a pump-turbine model with 20 guide vanes and 6 runner blades. The characteristic of the flow field varied corresponding to the operating conditions such as flow rate and rotational speed. Opening angles of guide vanes were kept uniform. A clockwise vortex was generated at inside of the runner blade under smaller rotational speed. A counterclockwise vortex was separated at the backside of the runner blade under higher rotational speed. At any operating conditions, the velocity between guide vanes and runner blades oscillated periodically at the blade passing frequency.

scholarly journals Numerical Analysis of a Model Pump-turbine Internal Flow Behavior in Pump Hump District

2014 ◽  
Vol 22 (3) ◽  
pp. 032040 ◽  
Author(s):  
Yao Yangyang ◽  
Xiao Yexiang ◽  
Zhu Wei ◽  
Zhai Liming ◽  
An Soo Hwang ◽  
...  
Keyword(s):  
Numerical Analysis ◽  
Flow Behavior ◽  
Internal Flow ◽  
Pump Turbine

Inter-Blade Vortex Characteristics With the Blockage Effects of Runner Blade in a Francis Hydro Turbine Model

2019 ◽  
Author(s):  
Seung-Jun Kim ◽  
Jin-Hyuk Kim ◽  
Young-Seok Choi ◽  
Yong Cho ◽  
Jong-Woong Choi
Keyword(s):  
Flow Rate ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Operating Conditions ◽  
Low Flow ◽  
Hydro Turbine ◽  
Runner Blade ◽  
Performance Reduction ◽  
Turbine Model ◽  
Low Flow Rate

Abstract This study presents the numerical analysis on the inter-blade vortex characteristics along with the blockage effects of runner blade in a Francis hydro turbine model with various flow rate conditions. The turbine model showed different flow characteristics in the runner blade passages according to operating conditions, and inter-blade vortex was observed at lower flow rate conditions. This inter-blade vortex can lead to performance reduction, vibration, and instability for smooth operation of turbine systems. The previous study on blockage effects on various runner blade thickness, showed its influence on hydraulic performance and internal flow characteristics at low flow rate conditions. Therefore, the inter-blade vortex characteristics can be altered with the blockage effects at low flow rate conditions in a Francis hydro-turbine. For investigating the internal flow and unsteady pressure characteristics, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes calculations are performed. These inter-blade vortices were captured at the leading and trailing edges close to the runner hub. These vortex regions showed flow separation and stagnation flow while blockage effects contributed for decreasing the inter-blade vortex at low flow rate conditions.

scholarly journals Analysis of Internal Flow Characteristics of a Startup Pump Turbine at the Lowest Head under No-Load Conditions

2021 ◽  
Vol 9 (12) ◽  
pp. 1360
Author(s):  
Wei Wang ◽  
Xi Wang ◽  
Zhengwei Wang ◽  
Mabing Ni ◽  
Chunan Yang
Keyword(s):  
High Speed ◽  
Pressure Pulsation ◽  
Working Condition ◽  
Guide Vane ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Operating Conditions ◽  
Small Range ◽  
Pressure Balance ◽  
Pump Turbine

The instability of the no-load working condition of the pump turbine directly affects the grid connection of the unit, and will cause vibration and damage to the components of the unit in severe cases. In this paper, a three-dimensional full flow numerical model including the runner gap and the pressure-balance pipe was established. The method SST k-ω model was used to predict the internal flow characteristics of the pump turbine. The pressure pulsation of the runner under different operating conditions during the no-load process was compared. Because the rotation speed, flow rate, and guide vane opening of the unit change in a small range during the no-load process, the pressure pulsation characteristics of the runner are basically the same. Therefore, a working condition was selected to analyze the transient characteristics of the flow field, and it was found that there was a high-speed ring in the vaneless zone, and a stable channel vortex was generated in the runner flow passage. Analyzing the axial water thrust of each part of the runner, it was found that the axial water thrust of the runner gap was much larger than the axial water thrust of the runner blades, and it changed with time periodically. It was affected by rotor stator interaction. The main frequency was expressed as a multiple of the number of guide vanes, that is, vanes passing frequency, 22fn. During the entire no-load process, the axial water thrust of the runner changed slowly with time and fluctuated slightly.

Effect of Runner Blade Thickness on Flow Characteristics of a Francis Turbine Model at Low Flowrates

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Seung-Jun Kim ◽  
Young-Seok Choi ◽  
Yong Cho ◽  
Jong-Woong Choi ◽  
Jin-Hyuk Kim
Keyword(s):  
Stokes Equations ◽  
Guide Vane ◽  
Vortex Formation ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Hydroelectric Power ◽  
Runner Blade ◽  
Blade Thickness ◽  
Interblade Vortices

Abstract Francis turbines are often used for generating hydroelectric power, but their performance characteristics significantly depend on the operating conditions. In particular, interblade vortices in the passages between runner blades can occur at low flowrates, which can degrade performance, and increase vibrations and instability during operation. In a previous study, we showed that the hydraulic performance and flow characteristics depend on the flow passage area of runner blades under low-flowrate conditions. Under such operating conditions, the runner blade thickness can affect the interblade vortex characteristics, and in turn, affect the performance of the turbine. In this study, we investigated the effect of runner blade thicknesses in the presence of interblade vortices under low flowrates; steady- and unsteady-state Reynolds-averaged Navier–Stokes equations were solved using a shear stress transport as a turbulence model. The interblade vortices were described well at the near leading and trailing edges near the hub. These vortex regions showed flow separation and stagnation flow, and the interblade vortex characteristics were dependent on the high-magnitude unsteady pressures at the low-frequency region. For the same guide vane opening, at lower flowrates, higher blockage ratios reduced interblade vortex formation and unsteady pressure.

Performance characteristics and internal flow patterns in a reverse-running pump–turbine

2011 ◽  
Vol 226 (3) ◽  
pp. 695-708 ◽  
Author(s):  
R Barrio ◽  
J Fernández ◽  
E Blanco ◽  
J Parrondo ◽  
A Marcos
Keyword(s):  
Stokes Equations ◽  
Internal Flow ◽  
Flow Patterns ◽  
Performance Characteristics ◽  
Centrifugal Pumps ◽  
Pump Mode ◽  
Modes Of Operation ◽  
Pump Turbine ◽  
Reverse Mode ◽  
Numerical Predictions

Vaneless centrifugal pumps are reversible turbomachines that can operate also as centripetal turbines in low and very low-head power plants. However, the general performance in reverse mode is difficult to predict since the internal flow patterns are different from pump mode and the performance characteristics are not usually provided by manufacturers. This article presents numerical and experimental investigations on the operation of a reverse-running pump–turbine. The numerical calculations were carried out by solving the full unsteady Reynolds-averaged Navier–Stokes equations with the commercial code Fluent for several flowrates between 20 per cent and 160 per cent of rated conditions and both modes of operation. A complementary series of experimental measurements were performed in a test rig in order to obtain the general characteristics of the machine in pump and turbine modes, with the purpose of validating the numerical predictions. Once validated, the numerical model was used to investigate the flow patterns at some significant locations by means of pressure and velocity contours, and also by vector maps. Additionally, the model allowed the estimation of the steady load on the impeller as a function of flowrate in both modes of operation. It was concluded that, while the radial load in reverse mode is three times smaller than in pump mode, the axial load can be up to 1.6 times larger.

scholarly journals Experimental research on flow field of a high head model pump turbine based on PIV test

2020 ◽  
Author(s):  
Demin Liu ◽  
Yongzhi Zhao ◽  
Weilin Xu
Keyword(s):  
Flow Field ◽  
Pressure Pulsation ◽  
Internal Flow ◽  
Operating Conditions ◽  
Head Model ◽  
Test Technique ◽  
Pump Turbine ◽  
Flow Angle ◽  
Operating Condition ◽  
Cavitation Pressure

Abstract Pump turbine operating conditions are complex, mainly including turbine mode and pump mode. Pump turbines have various instability problems during operation, such as S-shaped, pump hump, pressure pulsation and cavitation. PIV (Particle Image Velocimetry) is a very effective test technique for the internal flow field observation of pump turbines. In this paper, the internal flow field of pump hump, cavitation, pressure pulsation and four quadrants of the pump turbine are tested by PIV technology. The experimental observations show that the internal flow on those unstable working conditions of the pump turbine is extremely complicated. Those conditions which the vortex separation is serious and the flow angle is changed is far away the best efficiency working condition. Since the operating condition deviates from the optimal operating condition, the inflow Angle is changed and the inflow Angle is far away from the optimal inflow Angle.And the vortex induces and develops strongly by PIV test. The flow phenomenon are demonstrated at each operating points by PIV test.

Flow Pattern Evolution and Energy Decomposition of Flows at Different Operating Conditions in a Hydrodynamic Torque Converter

2016 ◽  
Author(s):  
Wei Wei ◽  
Mingxing Huang ◽  
Yu Li ◽  
Qingdong Yan
Keyword(s):  
Vortex Structure ◽  
Velocity Vector ◽  
Power Transmission ◽  
Flow Behavior ◽  
Internal Flow ◽  
Torque Converter ◽  
Operating Conditions ◽  
Speed Ratio ◽  
Energy Decomposition ◽  
Complex Flow

Power loss and flow blockage in turbomachinery such as hydrodynamic torque converter are usually caused by jet flow, second flow and flow separation. In this paper, the velocity vector and the pressure distribution of the internal flow field in hydrodynamic torque converter were reduced by the method of the Proper Orthogonal Decomposition (POD) to find the main flow structures and the energy decomposition in the passages of pump, turbine and stator. In order to find their evolutionary processes and energy decompositions, oil flow visualizations were conducted at different speed ratios from 0 to 0.8, including stall condition and design operating condition. The results showed that the first few modes containing the majority of energy could provide enough accuracy to predict flow behavior and flow structure in flow passages. Especially when the energy percentage of the first mode was majority, its vortex structures could be recognized easily. But the flow patterns of other modes were different from each other and they made the flow more turbulent and complex, which increases the energy loss in the process of power transmission. Besides that, the change of pressure gradient had a direct influence to velocity vector. The results also indicated that the observed fluid pattern of vortex structure became extensive while the influence of secondary flow decreased in the flow passage of pump with the increase of speed ratio. But the situation is just reversed in turbine, that is, the vortex disappeared gradually and the irregular turbulent flow appeared as the increase of speed ratio. In stator, the vortex structure emerged gradually when the speed ratio increased. So the method of snapshots is a very useful way to analyze the complex flow flied in depth and to predict the trend of development.

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