Transient Pressure Measurements on a High Head Model Francis Turbine During Emergency Shutdown, Total Load Rejection, and Runaway

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Chirag Trivedi ◽  
Michel J. Cervantes ◽  
B. K. Gandhi ◽  
Ole G. Dahlhaug
Keyword(s):  
High Amplitude ◽  
Francis Turbine ◽  
Scale Model ◽  
Head Model ◽  
Pressure Loading ◽  
Operating Life ◽  
Total Load ◽  
Unsteady Pressure ◽  
Emergency Shutdown ◽  
Turbine Runner

The penetration of intermittent wind and solar power to the grid network above manageable limits disrupts electrical power grids. Consequently, hydraulic turbines synchronized to the grid experience total load rejection and are forced to shut down immediately. The turbine runner accelerates to runaway speeds in a few seconds, inducing high-amplitude, unsteady pressure loading on the blades. This sometimes results in a failure of the turbine components. Moreover, the unsteady pressure loading significantly affects the operating life of the turbine runner. Transient measurements were carried out on a scale model of a Francis turbine prototype (specific speed = 0.27) during an emergency shutdown with a transition into total load rejection. A detailed analysis of variables such as the head, discharge, pressure at different locations including the runner blades, shaft torque, and the guide vane angular movements are performed. The maximum amplitudes of the unsteady pressure fluctuations in the turbine were observed under a runaway condition. The amplitudes were 2.1 and 2.6 times that of the pressure loading at the best efficiency point in the vaneless space and runner, respectively. Such high-amplitude, unsteady pressure pulsations can affect the operating life of the turbine.

Experimental Investigation of a High Head Francis Turbine During Spin-No-Load Operation

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Chirag Trivedi ◽  
Michel J. Cervantes ◽  
Ole G. Dahlhaug ◽  
B. K. Gandhi
Keyword(s):  
Transmission Lines ◽  
Swirling Flow ◽  
Pressure Sensors ◽  
Hydraulic Turbine ◽  
High Amplitude ◽  
Francis Turbine ◽  
Pressure Loading ◽  
Transient Pressure ◽  
Unsteady Pressure ◽  
Absence Of Power

Water passes freely through a hydraulic turbine in the absence of power requirements or during maintenance of the transmission lines, spillways, or dam. Moreover, the turbine operates under no-load conditions prior to generator synchronization during startup and after the generator disconnection from the grid load for shutdown. High-velocity swirling flow during spin-no-load (SNL) induces unsteady pressure pulsations in the turbine, and these pulsations cause fatigue in the blades. To investigate the amplitude of unsteady pressure loading, transient pressure measurements were carried out in a model Francis turbine during SNL. A total of six pressure sensors were mounted inside the turbine, i.e., one in the vaneless space, three on the blade surfaces, and two in the draft tube, and three discharge conditions were investigated over the operating range of the turbine. Analysis of the unsteady pressure data showed that the runner blades experience high-amplitude pressure loading during SNL. The amplitudes at all sensor locations were high compared with those under the normal operating condition of the turbine, i.e., the best efficiency point (BEP), and increased as the discharge through the turbine increased.

scholarly journals Investigations of unsteady pressure loading in a Francis turbine during variable-speed operation

2017 ◽  
Vol 113 ◽  
pp. 397-410 ◽  
Author(s):  
Chirag Trivedi ◽  
Einar Agnalt ◽  
Ole Gunnar Dahlhaug
Keyword(s):  
Francis Turbine ◽  
Variable Speed ◽  
Pressure Loading ◽  
Unsteady Pressure

Compressible Large Eddy Simulation of a Francis Turbine During Speed-No-Load: Rotor Stator Interaction and Inception of a Vortical Flow

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Chirag Trivedi
Keyword(s):  
Draft Tube ◽  
Numerical Study ◽  
Pressure Sensors ◽  
High Amplitude ◽  
High Energy ◽  
Outer Radius ◽  
Vortical Flow ◽  
Francis Turbine ◽  
Operating Life ◽  
Fatigue Development

This work investigates the unsteady pressure fluctuations and inception of vortical flow in a hydraulic turbine during speed-no-load conditions. At speed-no-load (SNL), the available hydraulic energy dissipates to the blades without producing an effective torque. This results in high-amplitude pressure loading and fatigue development, which take a toll on a machine's operating life. The focus of the present study is to experimentally measure and numerically characterize time-dependent pressure amplitudes in the vaneless space, runner and draft tube of a model Francis turbine. To this end, ten pressure sensors, including four miniature sensors mounted in the runner, were integrated into a turbine. The numerical model consists of the entire turbine including Labyrinth seals. Compressible flow was considered for the numerical study to account for the effect of flow compressibility and the reflection of pressure waves. The results clearly showed that the vortical flow in the blade passages induces high-amplitude stochastic fluctuations. A distinct flow pattern in the turbine runner was found. The flow near the blade suction side close to the crown was more chaotic and reversible (pumping), whereas the flow on the blade pressure side close to the band was accelerating (turbine) and directed toward the outlet. Flow separation from the blade leading edge created a vortical flow, which broke up into four parts as it traveled further downstream and created high-energy turbulent eddies. The source of reversible flow was found at the draft tube elbow, where the flow in the center core region moves toward the runner cone. The vortical region located at the inner radius of the elbow gives momentum to the wall-attached flow and is pushed toward the outlet, whereas the flow at the outer radius is pushed toward the runner. The cycle repeats at a frequency of 22.3 Hz, which is four times the runner rotational speed.

The Strength Analysis of Francis Turbine Runner Based on the Fluid-Solid Coupling

2014 ◽  
Vol 709 ◽  
pp. 41-45
Author(s):  
Kan Kan ◽  
Yuan Zheng ◽  
Xin Zhang ◽  
Bin Sun ◽  
Hui Wen Liu
Keyword(s):  
Water Pressure ◽  
Eastern China ◽  
Static Stress ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Strength Analysis ◽  
Maximum Deformation ◽  
The North ◽  
North Eastern ◽  
Turbine Runner

This paper does unidirectional fluid-solid coupling calculation on the runner strength under three designed head loading conditions of a certain Francis turbine in the north-eastern China. The water pressure on the blade in the flow fields of different operating conditions is calculated by means of CFD software CFX. With the help of ansys workbench, the water pressure is loaded to the blade as structural load to conclude the static stress distribution and deformation of the runner under different operating conditions. The results show that the maximum static stress increases with the rise of the flow and appears near the influent side of the blade connected to the runner crown; the maximum deformation increases with the rise of the flow and appears on the band. The results provides effective basis for the structural design and safe operation of the Francis turbine.

Two Phase PIV Measurements at the Runner Outlet in a Francis Turbine

2003 ◽  
Author(s):  
Monica Sanda Iliescu ◽  
Gabriel Dan Ciocan ◽  
Franc¸ois Avellan
Keyword(s):  
Francis Turbine ◽  
Cavitation Flow ◽  
Two Phase ◽  
Piv Measurements ◽  
Turbine Runner ◽  
Physical Insight ◽  
Complex Phenomena ◽  
Hydro Turbines ◽  
Operating Regimes ◽  
Averaging Techniques

Part load operation of hydro turbines with fixed pitch blades causes complex instable cavitation flow in the diffuser cone. Application of PIV systems provides the opportunity to investigate the flow velocity and turbulent fields in the case of development of cavitation vortex, the so-called turbine rope, at the outlet of a Francis turbine runner. The synchronization of the PIV flow survey with the rope precession allows to apply phase averaging techniques in order to extract both the periodic velocity components and the rope layout. The influence of the turbine setting level on the volume of the cavity rope and its center is investigated, providing a physical insight on the hydrodynamic complex phenomena involved in the development of the cavitation rope at Francis turbine operating regimes.

Fluid Force Moment on the Backshroud of a Francis Turbine Runner in Precession Motion

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Bingwei Song ◽  
Hironori Horiguchi ◽  
Yumeto Nishiyama ◽  
Shinichiro Hata ◽  
Zhenyue Ma ◽  
...  
Keyword(s):  
Flow Model ◽  
Swirl Flow ◽  
Francis Turbine ◽  
Leakage Flow ◽  
Fluid Force ◽  
Disk Rotation ◽  
Leakage Flow Rate ◽  
Turbine Runner ◽  
Force Moment ◽  
Axial Clearance

The fundamental characteristics of rotordynamic fluid force moment on the backshroud of a Francis turbine runner in precession motion were studied using model tests and computations based on a bulk flow model. The runner is modeled by a disk positioned close to a casing with a small axial clearance. An inward leakage flow is produced by an external pump in the model test. The effects of the leakage flow rate, the preswirl velocity at the inlet of the clearance, and the axial clearance on the fluid force moment were examined. It was found that the fluid force moment encourages the precession motion at small forward precession angular velocity ratios and the region encouraging the precession motion is affected by the preswirl velocity. Through the comparisons of the fluid force moment with and without the rotation of the disk, it was found that the normal moment without the disk rotation did not have the effect to encourage the precession motion. Thus, the swirl flow due to disk rotation was found to be responsible for the encouragement of the precession motion.

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