Experimental and Numerical Studies for a High Head Francis Turbine at Several Operating Points

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Chirag Trivedi ◽  
Michel J. Cervantes ◽  
B. K. Gandhi ◽  
Ole G. Dahlhaug
Keyword(s):  
Power Generation ◽  
Entire Range ◽  
Pressure Sensors ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Head Model ◽  
Numerical Studies ◽  
Pressure Time ◽  
Advection Schemes ◽  
High Head

Experimental and numerical studies on a high head model Francis turbine were carried out over the entire range of turbine operation. A complete Hill diagram was constructed and pressure-time measurements were performed at several operating conditions over the entire range of power generation by installing pressure sensors in the rotating and stationary domains of the turbine. Unsteady numerical simulations were performed at five operating conditions using two turbulent models, shear stress transport (SST) k-ω and standard k-ε and two advection schemes, high resolution and second order upwind. There was a very small difference (0.85%) between the experimental and numerical hydraulic efficiencies at the best efficiency point (BEP); the maximum difference (14%) between the experimental and numerical efficiencies was found at lower discharge turbine operation. Investigation of both the numerical and experimental pressure-time signals showed that the complex interaction between the rotor and stator caused an output torque oscillation over a particular power generation range. The pressure oscillations that developed due to guide vanes and runner blades interaction propagate up to the trailing edge of the blades. Fourier analysis of the signals revealed the presence of a vortex rope in the draft tube during turbine operation away from the BEP.

Numerical analysis of unsteady flow under high‐head operating conditions in Francis turbine

2010 ◽  
Vol 27 (3) ◽  
pp. 365-386 ◽  
Author(s):  
Xiao Yexiang ◽  
Wang Zhengwei ◽  
Yan Zongguo ◽  
Li Mingan ◽  
Xiao Ming ◽  
...  
Keyword(s):  
Numerical Analysis ◽  
Unsteady Flow ◽  
Operating Conditions ◽  
Francis Turbine ◽  
High Head

scholarly journals Experimental investigation on a high head model Francis turbine during load rejection

2016 ◽  
Vol 49 ◽  
pp. 082004 ◽  
Author(s):  
R Goyal ◽  
C Bergan ◽  
M J Cervantes ◽  
B K Gandhi ◽  
O G Dahlhaug
Keyword(s):  
Experimental Investigation ◽  
Francis Turbine ◽  
Head Model ◽  
High Head

Mitigation of Flow-Induced Pressure Fluctuations in a Francis Turbine Using Water Injection

2019 ◽  
Author(s):  
Muhannad Altimemy ◽  
Bashar Attiya ◽  
Cosan Daskiran ◽  
I-Han Liu ◽  
Alparslan Oztekin
Keyword(s):  
Power Generation ◽  
Turbulent Flow ◽  
Draft Tube ◽  
Pressure Fluctuations ◽  
Water Injection ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Partial Load ◽  
Flow Induced Vibrations ◽  
Dynamics Simulations

Abstract Computational fluid dynamics simulations are conducted to characterize the spatial and temporal characteristics of the turbulent flow fields inside Francis turbine operating at the design and partial load regimes. High-fidelity large eddy simulations turbulence model is applied to investigate the flow-induced vibrations in the draft tube of the unit. The water injection at 4% rate from the runner cone is implemented to control the flow-induced pressure fluctuations. The simulations are conducted at the turbine design point and two partial load operations with and without water injection. It has been demonstrated that the water injection has a profound influence in the turbulent flow structure and the pressure field inside the draft tube at the partial load operating conditions. To evaluate the effectiveness of the water injection techniques in mitigating flow-induced fluctuations, the probes at various locations along the wall of the draft tube are used to monitor the pressure signals. It appears to be a reduction in the level of pressure fluctuations by the water injection at both partial load operating regimes. However, we could not draw a firm conclusion about the level of mitigation of flow-induced vibrations. Simulations should be carried out for much longer flow time. Water injection hardly influenced the unit power generation. Hence water injection can be employed effectively without a major liability on the power generation.

Impact of Different Operating Conditions on the Dynamic Excitation of a High Head Francis Turbine

2016 ◽  
Author(s):  
Markus Eichhorn ◽  
Eduard Doujak
Keyword(s):  
Fatigue Analysis ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Fluid Structure Interactions ◽  
Cfd Simulations ◽  
Dynamic Excitation ◽  
Hydropower Plants ◽  
Rotor Stator Interaction ◽  
High Head ◽  
Strain Gauge Measurements

Fatigue analysis becomes more important in the design phase of Francis turbine runners due to the changing requirements on hydropower plants, affected by the increasing amount of volatile energy sources. Francis turbines are operated more often and over longer periods of time at off-design conditions to provide regulating power to the electric grid. The lifetime of a Francis runner depends mainly on the dynamic excitation induced by unsteady pressure pulsations like the rotor-stator interaction or draft tube vortex ropes. An approach using one-way coupled fluid-structure interactions has been developed and is now extended using unsteady CFD simulations as well as harmonic and transient FEM computations. The results are compared to strain gauge measurements on the according high head Francis turbine to validate the overall procedure. The investigations should be further used to perform a fatigue analysis and to examine the applicability for lifetime investigations on Francis machines with different specific speeds.

Vortex Rope Formation in a High Head Model Francis Turbine

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Rahul Goyal ◽  
Michel J. Cervantes ◽  
B. K. Gandhi
Keyword(s):  
Physical Mechanism ◽  
Swirling Flow ◽  
Draft Tube ◽  
Dynamic Pressure ◽  
Angular Position ◽  
Francis Turbine ◽  
Head Model ◽  
Stagnation Region ◽  
Vortex Rope ◽  
High Head

Francis turbine working at off-design operating condition experiences high swirling flow at the runner outlet. In the present study, a high head model Francis turbine was experimentally investigated during load rejection, i.e., best efficiency point (BEP) to part load (PL), to detect the physical mechanism that lies in the formation of vortex rope. For that, a complete measurement system of dynamic pressure, head, flow, guide vanes (GVs) angular position, and runner shaft torque was setup with corresponding sensors at selected locations of the turbine. The measurements were synchronized with the two-dimensional (2D) particle image velocimetry (PIV) measurements of the draft tube. The study comprised an efficiency measurement and maximum hydraulic efficiency of 92.4 ± 0.15% was observed at BEP condition of turbine. The severe pressure fluctuations corresponding to rotor–stator interaction (RSI), standing waves, and rotating vortex rope (RVR) have been observed in the draft tube and vaneless space of the turbine. Moreover, RVR in the draft tube has been decomposed into two different modes; rotating and plunging modes. The time of occurrence of both modes was investigated in pressure and velocity data and results showed that the plunging mode appears 0.8 s before the rotating mode. In the vaneless space, the plunging mode was captured before it appears in the draft tube. The physical mechanism behind the vortex rope formation was analyzed from the instantaneous PIV velocity vector field. The development of stagnation region at the draft tube center and high axial velocity gradients along the draft tube centerline could possibly cause the formation of vortex rope.

Sign in / Sign up

Export Citation Format

Share Document