Among the renewable energy sources, hydropower plays an important role by providing approximately 60% of the renewable electricity. Globally, there is a growing installed capacity of renewable energy sources. This, along with the energy policies to reduce greenhouse gas emissions promotes the development of alternative renewable energy sources such as solar and wind power. The penetration of intermittent energy sources seriously impacts the energy balance as well as the stability of the electrical grid. Therefore, it is required to guarantee a smooth integration of this share into the existing power grids. Hydraulic power plants are one of the key components to stabilize the electric grid. As a result, the extended operations and flexibility of hydraulic turbines increase, and hydraulic turbines are subject to unstable flow conditions and unfavorable load fluctuations at off-design operations. A better understanding of off-design and transient effects, particularly in full-scale hydraulic turbines, has the potential to provide new methodologies to predict the sources of load fluctuations on the runner and to mitigate issues associated with them. Such knowledge can increase turbine refurbishment time intervals and avoid structural failures in extreme cases.

This thesis aims to develop methodologies (i.e., experimental and numerical) to assess Kaplan turbines flow conditions and flow effects on the structure under different operational conditions. The work is divided into two parts; an experimental measurement campaign performed on a full-scale Kaplan turbine, Porjus U9, and a numerical investigation of fluid-structure interaction in the corresponding model turbine. In the measurement campaign, several operational conditions ranging from start-up, speed-no-load, steady-state, load variations, emergency shutdown, runaway, and stop were examined. Steady-state and load variation measurements were carried out under on-cam and off-cam conditions. The main objective was to investigate the effect of the operation conditions on the pressure and stain fluctuations on the runner as well as the strain variations on the shaft. This would lead to propose a measurement methodology in which the blade loading can be predicted by strain measurements on the shaft. The pressure and strain measurements on the runner showed that different sources of fluctuations corresponding to a specific operating condition, e.g. part load and start-up, resulted in load fluctuations on the runner blade. The region in the proximity of the runner blade hub was observed as the most critical in terms of high strain value. During a start-up sequence, the strain measurement on the shaft revealed that both guide vane opening, and runner blade’s angle have a great effect on the strain value on the shaft. A correlation between the blade and shaft measurements seems to exist.

The numerical simulations performed on the Porjus U9 model demonstrated that the added inertia and damping were important, whereas the stiffness was negligible. The dimensionless added polar inertia was 23%–27% of the reference value. Added damping significantly contributed to the moment at low excitation frequencies, whereas the inertia became dominant at higher frequencies. Considering the presence of multiple perturbations in the simulations, the added polar inertia could be assumed independent. Whereas, the interaction of the harmonics modified the added damping value, particularly at high perturbation frequencies.

An increase in the start/stop cycles of hydraulic turbines due to the penetration of intermittent renewable energy sources is important. Hydraulic instabilities that occur in hydraulic turbines during start/stops may cause structural issues in the turbine components. High-stress fluctuations on the runner blades are expected during start-ups due to the unsteady pressure loading on the runner blades. This paper presents experiments performed on a 10 MW prototype Kaplan turbine at the Porjus Hydropower Center during a start-up cycle. Synchronized unsteady pressure and strain measurements on a runner blade and axial, bending (in two directions) and torsion strain measurements on the shaft were performed. In addition, the general parameters of the turbine (e.g., rotational speed, guide vane opening and runner blade angle) were acquired. Low-frequency fluctuations (0–15 Hz) were observed in the pressure data on the runner blade after opening the guide vanes from the completely closed position. A higher strain value was observed on the strain gauges installed on the runner blade near the hub (200–500 μm/m ) compared to the ones near the shroud at the leading and trailing edge. The strain fluctuation level on the shaft decreased after loading the generator by further opening the guide vanes. Higher fluctuations were observed in the torsion strain compared to axial and bending strain. In addition, the torsion strain peak-to-peak value reached 12 times its corresponding value at 61% guide vane opening.

A water turbine runner is exposed to several perturbation sources with differentfrequencies, phases, and amplitudes both at the design and off-design operations. Rotor-statorinteraction, cavitation, rotating vortex rope, and blade trailing edge vortices are examples of suchperturbations which can disturb the runner. The rotor dynamic coefficients require beingdetermined to perform a reliable dynamic analysis. Fluid added inertia, damping, and stiffnesshave previously been investigated for individual perturbation frequencies for the torsionalvibration of a Kaplan turbine model runner. However, a number of perturbation sources mostlytake place simultaneously and alter the dynamics of the runner. Soltani et al. [1] have evaluatedthe torsional added parameters for a Kaplan turbine runner using numerical simulationsconsidering single perturbation frequency. In the present work, the fluid added parameters areassessed in the presence of multiple perturbation sources. A similar methodology is used. Asingle-degree-of-freedom (SDOF) model for the dynamic model and unsteady ReynoldsaveragedNavier–Stokes approach for the flow simulations are assumed. Perturbations withdifferent frequencies are applied to the rotational speed of the runner to determine the fluid addedparameters for the torsional vibration. A number of previously investigated frequencies arechosen and their combinations are investigated. In addition, two different phase shifts areconsidered between the applied perturbations to study the effect of phase. Two more test caseswith higher perturbation amplitude are also conducted to investigate its influence on the fluidadded inertia and damping. The results are compared with the previous study and the interactionof multiple perturbations on the added parameters is investigated.

Fluid added mass, damping, and stiffness are highly relevant parameters to consider when evaluating the dynamic response of a submerged structure in a fluid. The prediction of these parameters for hydraulic turbines has been approached relatively recently. Complex fluid-structure analyses including three-dimensional flow and the need for experiments during operation are the main challenges for the numerical and experimental approaches, respectively. The main objective of this review is to address the impact of different parameters, for example, flow velocity, cavitation, nearby solid structure, and rotational speed on the fluid added mass and damping of Kaplan/Propeller and Francis turbine runners. The fluid added stiffness is also discussed in the last section of the paper. Although studies related to hydraulic turbines are the main objective of this paper, the literature on hydrofoils is also taken into consideration to provide valuable information on topics such as individual runner blades. In this literature survey, the analytical, numerical, and experimental approaches used to determine fluid added parameters are discussed, and the pros and the cons of each method are addressed.

The impact of fluid on the runner of a hydraulic turbine is a recurrent problem. Fully coupled fluid-structure simulations are extremely time consuming. Thus, an alternative method is required to estimate this interaction to perform a reliable rotor dynamic analysis. In this paper, numerical estimations of the added inertia, damping and stiffness for a Kaplan turbine model runner are presented using transient-flow simulations. A single-degree-of-freedom model was assumed for the fluid-runner interaction, and the parameters were estimated by applying a harmonic disturbance to the angular velocity of the runner. The results demonstrate that the added inertia and damping are important, whereas the stiffness is negligible. The dimensionless added polar inertia is 23-27% of the reference value (ρR⁵). Damping significantly contributes to the moment at low excitation frequencies, whereas the inertia becomes dominant at higher frequencies.

The development of renewable energy sources has increased the need for power regulation. Power system regulation is mainly performed by hydropower plants through load variations. Additional forces are exerted on the runner blades during these load variations. This paper deals with pressure measurement performed on the blades of a Kaplan turbine model under steady state and load variation conditions. Flow behavior and frequency content of the pressure are investigated and compared to find critical condition in terms of pressure fluctuation. The results show that at various operating points and conditions, different regions of the blade are important. During load rejection, a considerable amount of pressure fluctuations are exerted on the runner blades. These results will be used to define experiments to be performed on the corresponding prototype. On the prototype, the loads acting on the runner blades will be investigated at various operation points similar to the model. In addition, the relation between the frequency content on the blades and loads on the main shaft will be investigated. Comparing results from model and prototype eventually would be valuable to explore the flow characteristics in prototype since CFD simulation of prototype is challenging.

There is a severe tendency to reduce weight and increase power of gas turbine. Such a requirement is fulfilled by higher pressure ratio of compressor stages. Employing tandem blades in multi-stage axial flow compressors is a promising methodology to control separation on suction sides of blades and simultaneously implement higher turning angle to achieve higher pressure ratio. The present study takes into account the high flow deflection capabilities of the tandem blades consisting of NACA-65 airfoil with fixed percent pitch and axial overlap at various flow incidence angles. In this regard, a two-dimensional cascade model of tandem blades is constructed in a numerical environment. The inlet flow angle is varied in a wide range and overall loss coefficient and deviation angles are computed. Moreover, the flow phenomena between the blades and performance of both forward and afterward blades are investigated. At the end, the aerodynamic flow coefficient of tandem blades are also computed with equivalent single blades to evaluate the performance of such blades in both design and off-design domain of operations. The results show that tandem blades are quite capable of providing higher deflection with lower loss in a wide range of operation and the base profile can be successfully used in design of axial flow compressor. In comparison to equivalent single blades, tandem blades have less dissipation because the momentum exerted on suction side of tandem blades confines the size of separation zone near trailing edges of blades.