background the pelton turbine is an old technology, but

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BackgroundThe Pelton turbine is an old technology, but there are still gaps in the knowledge concerning the flow within the turbine and the flow mechanisms that govern it.

To enable a greater possibility of collaboration within the researchers working on the Pelton turbine an open reference turbine has been designed and is used as the test case for the study of the flow.

The turbine will be fitted with an on board boroscope to enable inspection of the bucket within the rotating frame. The boroscope will be connected to a SA5 High Speed Camera that will make it possible to investigate the flow within the Pelton turbine relative to the turbine. This will again give the possibility to look closely at the flow mechanisms affecting the flow and possibly acquire the stream lines and relative velocities within the flow field.

PhD Thesis Waterpower Laboratory

Flow in Pelton Turbines

By Bjørn Winther Solemslie

Supervisor: Ole Gunnar DahlhaugCo-Supervisor: Torbjørn K. Nielsen

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BackgroundVarying demand for power requires turbines to be operated at part load more frequently, and turbines are subject to more frequent load variations than have been seen before. These conditions induce phenomena that can be difficult to simulate using CFD, due to lacking experimental data available.

The aim of this thesis is to experimentally investigate the phenomena occuring at off-design operation of a high head Francis turbine and during transient operation. The data produced will be submitted to the Francis-99 workshops, a series of workshops aiming at establishing the state-of-the-art for CFD simulation of Francis turbines. The results will also be used to determine the correlation between the transient flows occuring in the runner, and the crack porpagation in the runner caused by FSI.


High Head Francis Turbines

By Carl Bergan

Supervisor: Ole Gunnar Dahlhaug

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BackgroundUsing reversible pump turbines to regulate the power in the power market requires a quick change in the operating situation of the machine. This doctoral thesis aims to increase the effectiveness of the change from pump to turbine mode of operation.

• Allowing water to be the driving force in changing the operational situation without total shutdown of the machine.

The hypothesis is that this method can be done without bigger strain on the machine than a normal start stop sequence and with lower probability of experiencing instabilities.


Dynamics and Stability in Reversible Pump Turbines

By Magni Fjørtoft Svarstad

Supervisor: Torbjørn K. Nielsen

19

Background

Frequency analysis of a pressure pulsations in a Francis draft tube

Increased demand for flexibility in the power supply has lead to an increase in operation outside best efficiency point. Part load operation causes dramatic changes in the flow regime of the draft tube. For Francis turbines operating at part load, there is a mismatch between swirl generated by the guide vanes and the momentum extracted by the turbine runner. The vortex breakdown than occurring in the draft tube is recognized as the main cause of severe flow instabilities and pressure fluctuations. The consequences are known to be heavy vibrations and noise, which may cause high fatigue load and ultimately lead to mechanical failure. Mitigation of pressure pulsations is considered an imported task since it will increase the life time of the turbine.

Different methods for mitigating the vortex rope and the pressure fluctuations such as air injection, water injection, runner shaft extension have been investigated. The aim of this thesis is to further investigate these methods to find the best way of mitigating pressure pulsations.


Pressure Pulsations in Francis Turbines

By Peter Joachim Gogstad

Supervisor: Ole Gunnar Dahlhaug and Torbjørn K. Nielsen

20

BackgroundThe variations in the grid frequency in the Nordic countries have increased during the last years. The turbines are also more often operated at part load or maximum load. In this project these effects will be studied, to see if they can explain why some relative new Francis turbines have experienced problems with cracks.

The generator’s torque and the runner’s torque are acting in opposite direction, and this leads to stresses in the material of the runner.

These stresses will be studied with Fluid Structure Interaction (FSI) where the effects from both the fluid side and the structural side of the turbine are simulated.

Different things need to be considered:

• The speed droop of the turbine

• The variations in grid frequency

• Design of the conduit system

• The governor

• Design of the runner

• The operation plan for the unit


Dynamic Loads in Hydro Power Plants

By Rakel Ellingsen

Supervisor: Pål-Tore Storli

21

Background

Sediment erosion in Francis turbine components Design of test setup

Sediment erosion of turbine components has been a challenge for the hydro power plants under Himalayan and Andes basins. In Francis turbines, sediment erosion also causes increase of clearance between guide vanes and facing plates and cross flow occurs from the increased gap. This cross flow together with other secondary flows disturbs the velocity profile at the runner inlet. Change in velocity profile at the inlet causes additional erosion damage and other undesired effects in turbine runner. Examination of effects of increased cross flow from guide vanes on the flow conditions at the runner inlet will be main aim of this study.

Objectives1. Study of causes and effects of erosion in Francis turbine operating in sediment flow.

2. Develop a test setup to create the flow conditions between guide vanes and runner inlet of a high head Francis turbine.

3. Investigate the effects of leakage flow around the guide vanes of high head Francis turbines on velocity distribution at the runner inlet.


Sediment Erosion in Hydraulic Turbines

By Biraj Singh Thapa

Supervisor: Ole Gunnar Dahlhaug

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Fig. 1 Pressure pulsations developed in the vaneless space during the best efficiency operating point (BEP) and

runaway condition.

Fig. 2 swirling flow inside the blade passages during runaway operating

condition of the model Francis turbine.

Fig. 3 Unsteady pressure variation/pulsations in the vaneless space

during transition from steady state full load operating condition to the

total load rejection of the model Francis turbine

By Chirag Trivedi

BackgroundHydraulic turbines are used extensively to stabilize power grids because they can restart rapidly and/or change the power output before the grid collapses completely or black out. In recent years, a dramatic increase in grid-connected wind and solar power has resulted in problems related to power grid stability and reliability. Operating life of hydraulic turbines has been affected, as the

runner blades experience more fatigue.

Current workPresent work is related to the series of Francis-99 workshops, which are organized by NTNU and LTU. I am needed to perform experimental and numerical investigations on a model Francis turbine. The experimental investigations include both steady state and transient measurements. The work is also focuses on fluid structure analysis on the Francis runner. During this work, two-way coupling simulations will be performed.

The following objectives have been defined:

• CFD and mechanical analysis of the Francis turbine.

• Investigate the fatigue loading on the runner blades.

• Investigate the consequences of rotor stator interactions.

• Investigate the effects of added mass on the runners natural frequency.

Possible outcome:• Present investigations will provide more detailed information of the

unsteady pressure loading on the runner blades during steady state and transient operating conditions such as load acceptance, load rejection, startup, shutdown, and total load rejection.

• The numerical studies will provide more detailed information about the causes of runner crack and fatigue due to flexible operating trend of the hydraulic turbines.

• This will help to improve the runner design and sustain the power grid intermittency.


Fluid Structure Analysis of a Model Francis Turbine

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Background

Supervisor: Torbjørn Nielsen

By Erik Wiborg

Efficiency measurements are performed on hydro power plants from time to time. But having the efficiency measured continuously would benefit both operation and maintenance of the power plant.

Setting up a measurement system for hydraulic efficiency is a demanding task in its own, but the real challenge and the novelty of this work is the satellite systems that need to be in place.

Statkraft’s experimental system “Hydro BlackBox”, installed in Trollheim Power Plant is designed to do just that. It is this projects goal to tackle potential problems the system may encounter. The data must be check for stability in forehand of the computational process. The key measurement (flow), may need to be improved by means of merging the direct measurements with estimated values of the flow continuously through the use of the Kalman filter. Last but not last, an automated check and control system for the measured values will have to be designed to aid in the maintenance of the rather complex measurement set-up.


Turbine Monitoring and Data Processing With Focus on

The Kalman Filter

background the pelton turbine is an old technology, but

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