Influence of runner cone profile and axial water jet injection in a low head Francis turbine at part load

2022 ◽  
Vol 50 ◽  
pp. 101810
Author(s):  
Subodh Khullar ◽  
Krishna M. Singh ◽  
Michel J. Cervantes ◽  
Bhupendra K. Gandhi
Author(s):  
Yexiang Xiao ◽  
Zhengwei Wang ◽  
Jin Zhang ◽  
Guangjie Peng ◽  
Dingyou Liu ◽  
...  

The unsteady flow behavior and pressure fluctuations in the runner of a Francis turbine were predicted numerically for the middle-low head at three small guide vane openings. The unsteady Reynolds-averaged Navier-Stokes equations with the k–ω based SST turbulence model were solved to model the unsteady flow within the entire flow passage. The eddy characteristics inside the runner passage were discussed for various operating conditions, the shape of the blade channel vortex illustrate by the instantaneous iso-surfaces of the vorticity was similar with the experimental observation. This study investigates the characteristics of the unsteady flow dominant frequencies at different monitored points of the runner by spectrum analysis. At small guide vane opening conditions, the pulse in the runner flow passage are due to the rotor-stator interference between the runner and the guide vanes, the blade channel vortex in the runner blade passage. And the dominant frequencies of blade channel vortex were a low frequency. The unsteady flow behavior of blade channel vortex in the runner was classified numerically at part load of middle-low head.


2021 ◽  
Author(s):  
Subodh Khullar ◽  
Krishna M. Singh ◽  
Michel J. Cervantes ◽  
Bhupendra K. Gandhi

Abstract The presence of excessive swirl at the runner outlet in Francis turbines operating at part load leads to the development of flow instabilities such as the rotating vortex rope (RVR). The presence of RVR causes severe pressure pulsations, power swings, and fatigue damage in the turbine unit. Air and water injection in the draft tube have been reported to reduce the detrimental effects of RVR formation in the Francis turbines. Air injection is one of the oldest and most widely used methods. In contrast, water jet injection is a relatively new methodology. The present work reports the numerical simulations performed to compare the respective effectiveness of these methods to mitigate the RVR and the related flow instabilities. The efficacy of the two methods has been compared based on the pressure pulsations and pressure recovery in the draft tube cone. The results show that the air and water injection influence the draft tube flow field in different ways. Both air and water injection led to a reduction in pressure pulsation magnitudes in the draft tube cone. However, the air injection led to a negative pressure recovery while the water injection improved the draft tube action.


2017 ◽  
Vol 9 (2) ◽  
pp. 168781401769007 ◽  
Author(s):  
Pengcheng Guo ◽  
Zhaoning Wang ◽  
Longgang Sun ◽  
Xingqi Luo

According to several model test results of Francis turbines, complete model efficiency hill charts were constructed. The formation and inevitability of diversified hydraulic phenomena on model efficiency hill chart for typical head range were analyzed and the difference is compared, as well as characteristics and commonness toward the curves are discussed and summarized. Furthermore, hydraulic performance and geometric features are presented by particularly analyzing the efficiency hill charts. The inherent characteristics of Francis turbine is expressed by all kinds of curves on the model efficiency hill charts, and these curves can be adjusted and moved in a small range but cannot be removed out. Due to wide range of unit speed in terms of medium-low-head hydraulic turbines, incipient cavitation curve on suction side can be observed and it is positioned close to the operation zone; however, it fails to be visualized for the high-head turbine. The blade channel vortex curves are in the vicinity of optimum region for low-head hydraulic turbines, while high-head shows reverse trend. The interaction between zero incidence angle and zero circulation curve has a significant influence on isoefficiency circles. All comparisons and analyses could provide hydraulic design basis and retrofit references.


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