Ole Gunnar Dahlhaug

• PhD
• Professor (Full) at Norwegian University of Science and Technology

The global need for balance between energy generated from intermittent renewable sources and the actual demand has introduced severe operational challenges on hydropower, a steady energy source in the current context. Although it has some flexibility in operation by varying flow, head, and speed, the entirety of its operational range must be optimi...

Hydropower is one of the important sources of clean energy, where the use of the Francis turbine is the most than any other turbine. During off-design operations, turbines undergo significant fatigue loading, pressure pulsations, and vibration, which can be detrimental to the plant if operated for a long period of time. This paper aims to provide a...

Downstream hydropower plants, a change in water chemistry can lead to the occurrence of a widely unknown problem: total dissolved gas (TDG) supersaturation. It takes place when air is entrained in a water body and exposed to high pressures, which leads to gas dissolution in the water. Re-exposure to atmospheric pressure downstream the power plant r...

Secondary flows in Francis turbines are induced by the presence of a gap between guide vanes and top–bottom covers and rotating–stationary geometries. The secondary flow developed in the clearance gap of guide vanes induces a leakage vortex that travels toward the turbine downstream, affecting the runner. Likewise, secondary flows from the gap betw...

Sediment erosion is one of the major factors affecting the overall efficiency of hydro-turbines working under sediment laden conditions. The erosion not only decreases the efficiency but also changes the flow characteristics. However, the research regarding the changes in flow characteristics due to erosion is limited. The objective of this study i...

Labyrinth seals are important non-contact seals in Francis turbine. They help to reduce leakage flow from high to low-pressure regions. Therefore, this study focuses on the design of labyrinth seals providing more difference in pressure and minimum leakage flow. The 3-dimensional numerical models were built in one of the CAD software. The meshing a...

It is difficult to define a general relationship for discharge characteristics of a Pelton injector due to high degree of variability in geometry of injector amongst different Pelton turbine designs. This study has been aimed to determine discharge characteristics of injector of Pelton rig at Waterpower Laboratory, NTNU. Three different approaches...

This paper presents a comprehensive study of application of different machine learning techniques for the prediction of turbine faults in an early stage. As the need to ensure an optimal turbine operation through early stage fault detection grows, precise predictive models using machine learning techniques are also increasing rapidly. This study pr...

Pelton turbines, a commonly used impulse turbine for hydroelectric generation which converts the potential energy of the water into kinetic energy through a needle structure within the nozzle system. However, the exposure of the Pelton turbine components such as needle, seat ring, buckets to the sediment laden water can erode these components. The...

Hydro turbine operation far off from its best efficiency point introduces vortices and swirl that detaches flow from the blade surface. This break-off of flow accounts to loss in hydrodynamic lift accompanied by pressure fluctuations and vibration that leads to poor performance and mechanical failure of the turbine blades. Vortex generators (VGs) a...

In order to succeed in the transition to a more renewable energy sector, the hydropower industry must overcome multiple challenges in the coming decades, including the need for faster and reversible turbines to support emerging renewable energy sources. In addition, the location of new projects in tropical and semi-tropical areas poses unique consi...

Artificial total dissolved gas (TDG) supersaturation is a potentially lethal threat to the aquatic ecology downstream of hydropower plants. The severity of this threat dependents on the actual saturation level as well as on the duration of the event. Natural degassing is highly influenced by the river’s morphology and characteristics, and is in mos...

The hydro-turbines working in sediment-laden conditions often experience some material loss from their surface, which modifies the surface design. This material loss alters the mechanical strength of the turbine component as well as the corresponding flow phenomenon. These changes in the flow pattern can lead to efficiency losses, but they can also...

Anomaly detection in pumps is critical, especially in industrial applications. Industrial-scale pumps need to be replaced and maintained regularly. Anomaly detection can be used to forecast pump failure before it happens. Vibrational analysis has been utilized to non-intrusively ensure the effectiveness and safety of the machine’s functioning. When...

Most of the hydropower plants in Nepal are run-of-river type and over 60% of them are operating with Francis turbines. There are huge fluctuations in flow during the dry and wet seasons, which force the power plant owner to operate the turbines at off-design conditions which can induce cavitation and fatigue loads on the turbines. This study focuse...

As the world transitions towards more renewable energy sources, as a step to reduce the emissions of CO 2 , intermittent and non-dispatchable sources like solar and wind will take up a larger proportion of the energy production. With more unregulated power in the energy mix, a higher demand is put on the rest of the energy production system. Hydrop...

In Norway, a recent project used a risk matrix to identify about 200 hydropower plants ( 11 % of the total number) of being in high risk of producing air-supersaturated water. The combined installed capacity of these hydropower plants amounts to more than 45 % of Norway’s total installed hydropower capacity. Total dissolved gas (TDG) supersaturatio...

In this paper, we present the calibration setup, method, and results for a set of strain gauges installed on the trailing edge of the runner blades of a model Francis turbine. The calibration work is done as a step in the HydroFlex project, with the goal of taking experimental data to validate numerical models to better estimate the reduction in li...

In the development of a digital twin (DT) for hydropower turbines, dynamic modeling of the system (e.g., penstock, turbine, speed control) is crucial, along with all the necessary data interface, virtualization, and dashboard designs. Since the DT must mimic the actual dynamics of the hydropower turbine accurately, adaptive learning is required to...

In the development of a digital twin (DT) for hydropower turbines, dynamic modeling of the system (e.g., penstock, turbine, speed control) is crucial, along with all the necessary data interface, virtualization, and dashboard designs. Since the DT must mimic the actual dynamics of the hydropower turbine accurately, adaptive learning is required to...

Modeling and simulation constitute two important parts in constructing a sensible digital twin to mimic the dynamics of hydropower systems. Because of the physical nature of a hydropower system, the basic modeling should cover the water flow systems from the reservoir to the penstock (inlet water pipes), penstock to hydro turbine, and hydro turbine...

Hydro-abrasive erosion in hydraulic turbines is critical and one of the prominent issue due to its association with maintenance costs and production losses in the hydropower plant. IEC 62364:2019* standard guide focuses mainly on hydroelectric powerplant equipment and provides the standard on particle abrasion rates on several combinations like ope...

Convolutional Neural Networks are deep learning algorithms that are typically used for the classification of images. A black and white image can be represented as the number of rows and columns along with values of intensity for each of components of these rows and columns. Vibration measured with the help of accelerometer can be used to create an...

Sediment induced erosion in exposed components of hydraulic turbines is a major issue in most of the sediment laden hydropower projects. Gradual removal of material can change the components profile which can lead to change in flow characteristics and compromise in the efficiency as well. Among several components in Francis turbine, this study focu...

The use of Computational Fluid Dynamics (CFD) for predicting the flow behaviour in Pelton turbines is limited by the complex nature of the flow, interaction between the jets and interference of the water after the impact on the buckets. Besides, validation of the numerical results in such turbines is usually challenging due to the unsteadiness of t...

Sediment erosion in hydraulic turbines are severe in case of hydropower plants operating in Himalayan Rivers of Nepal. Francis turbine components are heavily eroded while hard particles as quartz flow along with water through the water conduit in power plant. In Francis turbines, the runner blades where significant portion of hydraulic energy conve...

Development of new hydropower projects in Himalayan regions aims for the efficient performance of the turbine with lesser operation and maintenance cost. Over the past two decades, significant efforts have been made to improve the sediment handling capabilities by the turbine components. In the case of Francis turbines, the design of guide vanes an...

This paper examines and discusses how various operation schemes and design philosophies can prolong the expected lifetime of a hydro turbine subjected to many start-stop cycles and high ramping rates. With the proliferation of renewable and non-dispatchable energy sources in Europe, a higher demand for flexible operation is put on the rest of the s...

The design of the Francis turbine aims to maximize its performance in terms of efficiency. This design approach has overlooked effects on the turbine due to sediment erosion for power plants operating under high sediment load. In this paper, a multi-objective design procedure to develop a Francis turbine runner for maximizing efficiency, as well as...

The complex geometry of Francis turbine components can be defined parametrically so that automatic optimization techniques based on parametrization can be used. This is convenient for a hydraulic redesign of individual turbine elements. Considering the importance of the guide vane cascade in defining the flow entering the runner, a parametric desig...

A clearance gap (CG) between guide vanes (GVs) and facing plates exists at both ends of a Francis turbine and allows the opening angle to be adjusted for varying operating conditions. Leakage flow is induced through this gap due to the pressure difference between the two sides of the guide vanes. While some research works have used qualitative appr...

The Francis-99 low specific speed Francis runner has undergone much study in the years since it was first made available to the public. The High Head Francis(HiFrancis) project, hosted by the Waterpower Laboratory at NTNU, have conducted multiple experimental campaigns to supply validation data for numerical simulations of the RSI phenomenon for th...

Wear and tear of hydraulic turbine due to sediment erosion is one of the major problems in hydropower plants located in the Himalayan and Andes regions. High sediment concentration in water of such areas wears down the mechanical components rapidly which causes significant operational challenges. In the present work, a prototype high head Francis r...

This paper is focused on the guide vane cascade as one of the most crucial stationary sub-systems of the hydraulic turbine, which needs to provide efficient inflow hydraulic conditions to the runner. The guide vanes direct the flow from the spiral casing and the stay vanes towards the runner, regulating the desired discharge. A parametric design to...

The problem of material erosion in hydraulic machineries has been under the investigation since a century ago. However, the proper solutions to the erosion of hydro turbine due to sediment-laden flows has not been found yet. The new and future hydropower development is shifting towards Asia region, which holds the highest capacity of undeveloped hy...

Hydropower is facing new operational strategies as the increasingly competitive power market demands for higher flexibility. Consequently, turbines are forced to handle tougher operation and are prone to more frequent degradation. By implementing a real-time monitoring system, a better understanding of the behavior of components may contribute to d...

Previous studies suggested variable speed operation of Francis turbines as a measure to improve the efficiency at off-design operating conditions. This is, however, strongly dependent on the hydraulic design and, for an existing turbine, improvements can be expected only with a proper redesign of the hydraulic surfaces. Therefore, an optimization a...

Impulse turbines are widely used in hydropower plants around the world due to their high efficiency in a larger operating range compared to reaction turbines. State of the art Pelton turbines can give over 90% efficiency at the designed operation load. However, there lies a possibility of improving the efficiency at off design condition for these t...

Hydropower plays an essential role in maintaining energy flexibility. Modern designs focus on sustainability and robustness using different numerical tools. Automatic optimization of the turbines is widely used, including low, mini and micro head turbines. The numerical techniques are not always foolproof in the absence of experimental data, and he...

Over the last years, several breakdowns in hydropower plants with low specific speed Francis runners have been reported. One of the main excitation forces in such runners is the pressure fluctuations originating from the rotor stator interaction. In this paper, the rotor-stator interaction has been analyzed utilizing pressure sensors onboard the ru...

In the published article [1] there is an error in the listing of the last author. “Dahlhaug G. Ole” should be “Ole Gunnar Dahlhaug” as listed in this erratum.

Variable-speed operation of a hydro turbine is considered as an alternative option to meet fluctuating energy demand as it allows high-ramping rate. Cavitation can be a limiting factor to utilize the variable-speed technology at full potential in a hydro power plant. This work investigates the cavitation characteristics and unsteady pressure fluctu...

Control valves, nozzles and other mechanical flow constricting constructions often introduces highly turbulent flow downstream of vena contracta. When solid particles are present in the fluid stream erosion can occur due to the high fluid velocity and turbulence, both in the converging and diverging section of a constriction. This paper presents an...

Nepal is a developing country with a literacy rate of 64.7% in 2015, which is a significant rise from 20.6% in 1981. About 10 % of the population have excess to university education in Nepal. Among the total population receiving a university education, those getting engineering education is below 2%. Nepal has the second largest hydropower potentia...

This paper presents results from an ongoing research project on extreme upgrading of existing hydropower systems. The project, AlternaFuture, studies how an existing hydropower system can be upgraded with a tripling or more of the installed capacity including pumped storage and at the same time improving the environmental conditions in the river ba...

This paper summarizes the development of a test rig containing three guide vanes of a Francis turbine, whose flow field is set up to match with that of the actual turbine. The rig is made suitable for Particle Image Velocimetry (PIV), such that the flow field around guide vanes can be measured. It has been studied that using three consecutive guide...

Erosion in guide vanes (GVs) has been reported from several power plants in Himalayan and Andes basins which affects the efficiency of turbine. Wear in clearance gaps (CGs) increases with the sediments passing through them resulting in increased gap size, which disturbs the flow into the runner inducing more losses. This paper investigates the flow...

The ability to predict a francis runners dynamic response to the exciting forces is paramount to avoid unwanted disintegration of the turbines components. In this article, each of the principal factors contributing to the dynamic response of the runner; eigenfrequency, mode shape, damping and pressure force, is individually examined and compared to...

Due to thinner blades and higher demands for flexibility, the high-head Francis runners designed today face considerable challenges that severely affect the runners’ expected lifetime. For many high-head Francis runners, the leading cause of fatigue is blade cracking due to Rotor-Stator Interaction, which cause vibrations in the runner blades. Accu...

Francis-99 is a series of three workshops, which provides an open platform to the hydropower researchers. It gives the possibility to explore capabilities/skills on futuristic turbine design and development. Under the Francis-99 test cases, complete design and data of a Francis turbine are provided. The measurements are conducted on state-of-the-ar...

The present work compares numerically predicted hill chart to experimental measurements of a Francis turbine. The main objective is to create a model for recreating hill charts using computational fluid dynamics (CFD). Accurate prediction of hill charts are useful in the design stage of production and may result in a more efficient runner. The prim...

The paper presents the recent trends and ideas for flexible operation of Francis turbines using Full-Size Frequency Converter (FSFC) or Doubly-Fed Induction Machine (DFIM) technology for variable-speed operation. This technology allows for the speed of the runner to be adjusted in order to maximize the efficiency and/or reduce dynamic loads of the...

The Norwegian power system today includes a relatively large percentage of Francis turbines with a head of above 300m, in the world. This leads to a need to maintain and develop the national competence regarding the challenges connected to this type of turbine. The importance of this competence is increased by the fact that these turbines have a hi...

As Francis turbines are chasing a higher efficiency, while trying to accommodate a wider load region, turbine blade fatigue is becoming a more pronounced problem. Details of the Fluid-Structure Interaction (FSI) between the turbine blades and the passing water is necessary to accurately predict the dynamic behavior of a runner in the design phase....

Erosion is a challenge in a wide range of industries where fluid is transferred through pipes, valves and other mechanical arrangements. Wear can occur due to a variety of mechanisms but is often related to the presence of droplets or solid particles in the fluid stream. This article presents a study of flow relevant to solid particle erosion in a...

The paper presents result from model measurements of the efficiency and pressure pulsation intensities for two low-specific-speed hydraulic turbines operated at variable speed, namely, one splitter-bladed Francis turbine marked with "F99" and one reversible pump-turbine marked with "RPT" and operated in a turbine mode. Both turbines have similar sp...

Repair/maintenance issue in power plants of Nepal is one of the major concerns, which has become an obstacle for smooth power generation. The rivers in Nepal contain excessive sediments, which is carried into the turbine causing erosion of several electro-mechanical components. The problem is more severe in wet season, when the concentration of sed...

In Guide Vanes (GV) of Francis turbines, a portion of the pressure head of water converts into velocity head. This causes high acceleration of the flow in GV before reaching the runner. Furthermore, GVs are accompanied with a small clearance gap at both ends to adjust the opening angle based on various operating conditions. In the case of sediment...

The present work investigates the unsteady pressure fluctuations in a model Francis turbine that are observed during steady state operation. Focus of the present study is to correlate pressure fluctuations between stationary and rotating components in the turbine. It is challenging and expensive to perform pressure measurements inside the rotating...

Over the last years, there have been several incidents with cracks in high head Francis turbines. These cracks are understood to be related to pressure pulsations, vibration modulus and the combination of these. In this paper, a setup for the investigation of pressure pulsations ina low specific speedmodel turbine is presented with the use of onboa...

The rotor stator interaction in a low specific speed Francis model turbine and a pump-turbine is analyzed utilizing pressure sensors in the vaneless space and in the guide vane cascade. The measurements are analyzed relative to the runner angular position by utilizing an absolute encoder mounted on the shaft end. From the literature, the pressure i...

An analysis of the pressure in a runner channel of a low-specific speed Francis model runner during resonance is presented, which includes experiments and the development of a pressure model to estimate both the convective and acoustic pressure field from the measurements. e pressure was measured with four pressure sensors mounted in the runner hub...

The Horizon 2020 Project ‘Increasing the value of Hydropower through increased Flexibility (HydroFlex)’ aims towards scientific and technological breakthroughs to enable hydropower to operate with very high flexibility in order to utilise the full power and storage capability. The project will create the environmental, social and technical basis fo...

This corrects the article “Experimental investigations of transient pressure variations in a high head model Francis turbine during start-up and shutdown” in volume 26, issue 2 on page 277. In the published article “Vaginal adhesions in a woman with the history of dystocia. Journal of Hydrodynamics, 2014, 26(2): 277–290. 10.1016/S1001-6058(14)60031...

Abrasive wear in the clearance gap of guide vanes (GVs) increases the gap size, which deteriorates the flow and causes loss of efficiency. This paper investigates the performance of a Francis turbine including erosion-induced clearance gaps on the GVs. The effect of the gap on the performance of the turbine is studied numerically, by using the GV a...

The present study aims to investigate the unsteady flow phenomenon that produces high energy stochastic fluctuations in a highly skewed blade cascade. A complex structure such as a turbine is operated at runaway speed, where the circumferential velocity is dangerously high, and the energy dissipation is so significant that it takes a toll on the op...

Sediment erosion of the hydropower turbine components is one of the key challenges due to the constituent of hard particles in the rivers of Himalayas and Andes. In these regions, Quartz is found as a main constituent (more than 50%), along with feldspar and other hard minerals. These particles have hardness more than 5 Moh’s scale, which is capabl...

Erosion on hydro turbine mostly depends on impingement velocity, angle of impact, concentration, shape, size and distribution of erodent particle and substrate material. In the case of Francis turbines, the sediment particles tend to erode more in the off-designed conditions than at the best efficiency point. Previous studies focused on the optimiz...

Smeland power plant in Norway is experiencing pressure pulsations in their Francis turbine when running above best efficiency point. By measuring both the pressure pulsations and runner efficiency, the cause and effect of the pulsations are to be investigated thoroughly, which is this works main purpose. To find the Francis runners efficiency the t...

The paper presents a simplified one-dimensional calculation of the efficiency hill-chart for Francis turbines, based on the velocity triangles at the inlet and outlet of the runner's blade. Calculation is done for one streamline, namely the shroud streamline in the meridional section, where an efficiency model is established and iteratively approxi...

This paper presents the preliminary work of the master thesis of the author, written at the Norwegian University of Science and Technology. Today, many Francis turbines experience formations of cracks in the runner due to pressure pulsations. This can eventually cause failure. One way to reduce this effect is to change the operation point of the tu...

Erosion is a challenge in many industries where fluid is transferred through pipe and valve arrangements. Wear can occur in a variety of systems and is often related to the presents of droplets or solid particles in the fluid stream. Solid particles are in many cases present in hydropower systems, and can cause severe damage to system components. F...

A post processing method has been developed to enable the extraction of quantifiable data from images captured from within the rotating frame of reference of a Pelton turbine. The turbine tested was the reference Pelton runner, designed at the Waterpower Laboratory (NTNU). The method relies on interpolation to 3D map the inner hydraulic surface of...

A hydrofoil resembling a high head Francis runner blade was submerged in a rectangular channel and attached to the walls in a fixed-beam configuration. The hydrofoil was excited by piezoelectric Macrofiber composite actuators (MFCs), and the vibration was measured at the trailing edge with Laser Doppler Vibrometry (LDV) and semiconductor strain gau...

Sediment constitutes several mineral compositions depending upon the geological formation and geography. In many of the rivers in Himalayas and Andes, Quarz is found as a main constituent (more than 50%), along with feldspar and other hard minerals. These particles have hardness more than 5 Moh’s scale, which is capable to erode turbine components....

This work investigates the unsteady pressure fluctuations in a hydraulic turbine that are observed during a dangerous case of steep load ramping interrupted by an unexpected transition into total load rejection. Although hydraulic turbines are expected to experience such events only a few times over their lifetime, the resulting pressure amplitudes...

This work investigates the unsteady pressure fluctuations in a hydraulic turbine that are observed during steep ramping. Although hydraulic turbines are expected to operate seamlessly during steep ramping, the resulting pressure amplitudes are so significant that they take a toll on a machine's operating life. Objective of the present study is to i...

A guide vane cascade is developed for the study of flow in the distributor of a low specific speed Francis turbine. Velocity and pressure measurements are done with Reynold’s number 1.15E+07, at 80% of BEP flow as in a reference prototype turbine. This work illustrates the development of test setup and focuses on investigation of PIV methods applie...

Hydropower is one of the most reliable renewable sources of electricity generation. With high efficiency and good regulating capacity, hydropower has the ability to meet rapid changes in power demand. Large investments in intermittent renewable energy resources have increased the demand for balancing power. This demand has pushed hydraulic turbines...

This work investigates the unsteady pressure fluctuations in two prototype Francis turbines during load variation and start-up. Although hydraulic turbines are expected to experience such events over their lifetime, the resulting pressure amplitudes are so significant that they take a toll on a machine's operating life. The interest of the present...

The study of wear in hydraulic turbines is taking place for over a century. However, geographical diversity of each region, need of tailor-made designs for different sites and several unsteady phenomena inside a turbine is causing hindrance for developing sediment-resistant turbines. Nevertheless, some recent studies have shown possibilities of min...

CFD has played a significant role to investigate the performance and improve the design of hydraulic turbines; however, the improvement of CFD method demands powerful computer resources including time, CPU, memory, and commercial licenses. In present work, both global and local parameters of a high head Francis turbine were studied using several ge...