Numerical Investigations of the unsteady Flow in a high-head Francis Turbine using FOAM-extend

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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Experimental investigations of transient pressure variations in a high head model Francis turbine during start-up and shutdown

Journal of Hydrodynamics ◽

10.1016/s1001-6058(14)60031-7 ◽

2014 ◽

Vol 26 (2) ◽

pp. 277-290 ◽

Cited By ~ 44

Author(s):

Chirag Trivedi ◽

Michel J. Cervantes ◽

B. K. Gandhi ◽

Dahlhaug G. Ole

Keyword(s):

Francis Turbine ◽

Experimental Investigations ◽

Head Model ◽

Transient Pressure ◽

Start Up ◽

High Head

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Investigating the Performance of a Super High-head Francis Turbine under Variable Discharge Conditions Using Numerical and Experimental Approach

Energies ◽

10.3390/en13153868 ◽

2020 ◽

Vol 13 (15) ◽

pp. 3868 ◽

Cited By ~ 3

Author(s):

Zheming Tong ◽

Hao Liu ◽

Jianfeng Ma ◽

Shuiguang Tong ◽

Ye Zhou ◽

...

Keyword(s):

Draft Tube ◽

Numerical Models ◽

Guide Vane ◽

Maximum Velocity ◽

Francis Turbine ◽

Inlet Pipe ◽

Guide Vanes ◽

Flow Acceleration ◽

High Head ◽

Reduced Scale

A super high-head Francis turbine with a gross head of nearly 700 m was designed with computational fluid dynamics (CFD) simulation and laboratory tests. Reduced-scale (1:3.7) physical and numerical models of the real-scale prototype were created to investigate the hydraulic performance. According to the CFD analysis, a strong rotor–stator interaction (RSI) between guide vanes and runner blades is observed as a result of the high-speed tangential flow towards runner created by the super high water head as well as the small gaps between the radial blades. At the designed best efficiency point (BEP), there is no significant flow recirculation inside the flow passage and minor loss occurs at the trailing edge of the stay vanes and guide vanes. Maximum velocity is observed at runner inlets due to flow acceleration through the narrow passages between the guide vanes. The elbow-shaped draft tube gradually decreases the flow velocity to keep the kinetic energy loss at a minimum. The laboratory test was conducted on a reduced-scale physical model to investigate the pressure pulsations and guide vane torque (GVT) under variable-discharge configurations, which are key concerns in the design of a high head turbine. Pressure sensor networks were installed at the inlet pipe, vaneless space and draft tube, respectively. The most intense pressure variation occurs at the inlet pipe and elbow at 0.04–0.2 GVOBEP and 1.5–1.8 GVOBEP with a low frequency about 0.3 times of the runner frequency, while the vibration in vaneless zone performs stable with the blade passing frequency caused by RSI. The GVT shows a declining trend and then keeps stable as GVOs increases at synchronized condition. For the misaligned conditions, the torque of adjacent guide vanes differs a lot except at the synchronous angle and maximum absolute value at least doubles than the synchronized condition.

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