Full Turbine Research Articles

Optimal Environmental Siting of Future Wind Turbines in the North Sea.

Offshore wind energy (OWE) represents a key technology for achieving a sustainable energy transition. However, offshore wind farms (OWFs) can impact the environment via installation, operation, maintenance, and decommissioning activities together with the raw materials and energy required for their manufacturing. This study assesses the material and carbon footprint of potential OWF locations in the North Sea for various possible future technology developments. We find that better sitings could save up to ∼0.11 kg (∼65%) of steel, ∼ 0.16 g (∼31%) of copper, and ∼6.44 kg (∼26%) of embodied CO2-eq per MWh of electricity produced compared to the status quo setups. Nearshore regions of the North Sea, particularly the eastern and northwestern areas, have the lowest CO2-eq per MWh of electricity produced due to favorable wind resources. Developing an OWF in the central North Sea requires more copper and aluminum due to large distances to shore and thus incurs higher embodied CO2-eq per MWh. These areas also overlap with several protected areas and thus remain the least favorable for OWE development. The future emergent OWE technological developments for 2040 such as the installation of larger turbines with an extended lifetime alone could, on average, lead to reductions of ∼0.06 kg in steel demand (∼35%), ∼ 0.15 g in copper demand (∼31%), and ∼10.97 kg of CO2-eq (∼41%) per MWh produced. Future OWFs incorporating these technological developments, when placed in the most suitable locations, have the potential to substantially lower OWF environmental impacts across the full turbine life cycle.

Numerical analysis and runner shape optimization of a high head pump-turbine

Abstract A set of numerical approaches ranging from the time-consuming unsteady full turbine RANS approach to a very fast periodic steady-stage approach were considered for CFD simulation of flow in Francis pump-turbines. Their computational efforts and accuracy of efficiency prediction were assessed through comparison with experimental data in both pump and turbine modes. It was shown that the unsteady full turbine approach is needed for accurate simulation of low discharge regimes in pump mode. From the other hand, near the optimum and in the high discharge zone, periodic steady-stage approach can be utilized. Next, an approach for multi-objective runner shape optimization of pump-turbine runners was proposed. Thirty free design parameters allowed flexible variation of runner blade shape, hub and band curves, as well as the height of the distributor, linked to the guide vane opening angle. Two or three reference operating points, indicating the turbine performance and head in both turbine and pump modes, were taken for optimization. Cavitation characteristics were accounted for through special constraints. The approach was tested for a 500 m head pump-turbine. It was shown that the optimized runners significantly outperform the initial one in terms of efficiency with comparable cavitation performance.

Design and analysis of a single-stage supersonic turbine with partial admission

Supersonic impulse turbines are commonly used to harvest waste heat from systems based on organic Rankine cycles, automotive applications, and gas-generator liquid rocket engines. This research aims to design and analyze a single-stage supersonic turbine with a rated power of approximately 440 KW. We present a comprehensive preliminary design roadmap followed by design parameters optimization. The preliminary sizing is carried out using one-dimensional flow analysis, while the blade geometrical design is performed using the two-dimensional method of characteristics. The turbine performance is then analyzed through numerical simulations on three-dimensional models. Comprehensive parametric analyses are conducted to examine the turbine performance sensitivity to changes in partial admission (PA), mean radius, and turbine blade height using three-dimensional sliding mesh techniques (SMT). The current analysis simulates the full turbine to capture PA effects, rather than focusing on a single periodic sector as is common in turbomachinery simulation practices. Different PA scenarios are investigated, emphasizing a single rotor passage over a complete rotor cycle in a partially admitted turbine, and examining its charging and discharging mechanisms. Flow tracking over such a blade shows that the turbine rotor exhibits compressor-like behavior over most of the unadmitted zone, contributing to efficiency drops and severe transients.

Comparison of helix and wake steering control for varying turbine spacing and wind direction

A variety of wind farm control strategies exist in order to reduce unfavorable wake effects in large wind farms. While strategies like wake steering already reached a high maturity level, it is interesting to compare them to more recently proposed strategies. Such a comparison can form the basis for the development of a symbiotic wind farm control toolbox, from which a control strategy is chosen and activated depending on the operating conditions. The present study compares wake steering with helix control across a wide range of turbine spacings and wind directions using large-eddy simulation (LES). The size of the search space is made computationally tractable for LES by adopting a setup based on one physical upstream turbine and a distribution of virtual downstream turbines which do not exert any thrust force. It is found that helix control is beneficial for full wake overlap and turbine spacing of less than six rotor diameters whereas wake steering proves to be optimal further downstream and for partial wake overlap. Furthermore, the results show that the helix control setpoint in the proximity of full wake overlap scenarios is less susceptible to wind direction variations. This finding indicates that the combination of wake steering and helix control has potential for the design of a wind farm controller which is more robust in full wake overlap scenarios and can reduce the need for large yaw offset adjustments.

A semi-empirical model for time-domain tower Vortex induced Vibration load simulations of wind turbines

A new method for simulating aeroelastic resonances between vortex shedding and structural eigenfrequencies of a wind turbine tower is presented in this publication. This aero-elastic effect of Vortex induced Vibrations (ViV) has the potential to disrupt installation processes and cause fatigue and extreme loads on the tower. Despite this issue, there are no established simulation methods available in literature, able and sufficiently efficient to predict the ViV in turbulent and site specific design load conditions. This state-of-the-art is extended by introducing an efficient semi-empirical, time-domain simulation method, which is capable of analyzing the tower ViV excitations and aeroelastic responses in wind turbine load simulations of the isolated tower or the full turbine for fatigue and extreme loads. The method is based on an adaptive harmonic equation, which is automatically tuned to the instantaneous tower motions.

Investigation of Nonlinear Effects in the Tower Structure of Wind Turbines and Their Influence on System Behavior

In multibody simulation (MBS) software, large structural components such as the tower are often modeled as flexible bodies using the Craig-Bampton method. While being very computationally efficient, nonlinear effects cannot be modelled in this way. The flange connections between the segments of tubular steel towers are one such source of nonlinearity. The magnitude of this nonlinearity increases with damages at the flanges as flange gaping becomes more common. The nonlinearities in the flanges lead to a changing stiffness and hence changing eigenfrequencies of the structure as a function of its deformation. In this paper, a nonlinear model of a tower with and without damages is being developed and validated based on an FEM model. The model is assembled from linear flexible bodies linked with nonlinear rotatory springs. The damages considered are broken bolts as well as axially symmetric angular flange gaps. It is shown that the MBS model closely emulates the FEM model including all nonlinear effects. The nonlinear tower model is incorporated into an existing MBS model of a commercial wind turbine in the 4 MW range. The eigenfrequencies of the full turbine model are being calculated using the build-in eigenvalue solver in Simpack. The results show a small but measurable decrease in eigenfrequencies compared to the linearized model, which scales with the extend of the damage.

Systemic optimal design of wind energy generator based on combined analytical-finite element method using genetic algorithms

This work deals with optimal systemic design of wind energy generator based on an Integrated Optimal Design (IOD) methodology of a full passive wind turbine system. The originality of the study resides in the use of DC model of wind turbine the make the integration of this model to Genetics Algorithms method possible. The optimization problem concerns the association of the DC model of the wind turbine with a developed Genetics Algorithms to optimize conjointly the global power system mass and total power system energy losses with several constraints. The generator is designed by analytical method validated by finite element method.

Vortex-induced vibrations of wind turbines: From single blade to full rotor simulations

Vortex-induced vibrations (VIVs) of wind turbine blades are a phenomenon that cannot be predicted sufficiently accurate by low fidelity methods. High fidelity methods, such as computational fluid dynamics (CFD) coupled to a structural solver come at a high computational cost. Most studies of the phenomenon have so far focused on analysis of single blades. For these cases, the so-called forced-motion method of prescribing the blade motion according to structural modeshapes has proven effective.In this article, VIVs of the IEA 10 MW reference turbine is studied in a fluid–structure interaction setup, where the structural dynamics of the full turbine are represented in the structural solver and the full rotor aerodynamics are simulated in the CFD solver. Due to the high computational cost this study is limited to only a single case with the rotor in bunny configuration, 80 degrees pitch and 90 degrees yaw. Also the purely structural power dissipation of the full turbine is studied to enable full rotor forced-motion in future work. A blade tip amplitude of roughly 17 meters is reached in the full turbine simulations, which is a significantly larger limit cycle amplitude than what would be reached in a corresponding isolated single blade simulation. The analysis also shows that forced-motion simulations combining three single blades vibrating according to the structural modeshape would be feasible. It is further observed, that the power injection or extraction close to the blade tip may change drastically at very large amplitudes compared to lower amplitudes.

Qualitative Investigation of Wake Composition in Offshore Wind Turbines: A Combined Computational and Statistical Analysis of Inner and Outer Blade Sections

High-fidelity numerical simulations are used to thoroughly analyze the evolution of the wake behind a megawatt-scale offshore wind turbine. The wake features are classified in terms of wake dynamics composition and the associated turbulence characteristics originating from the inner and outer sections of the blades. Understanding the wake is essential for developing compact layouts for future wind farms. We employed a transient Sliding Mesh Interface (SMI) technique to analyze the fully dynamic wake evolution of the offshore NREL 5MW full turbine. Our high-fidelity results have been validated against previously published results in the literature. We thoroughly investigated the dominant structures of the wake using Proper Orthogonal Decomposition (POD) techniques, which we applied to transient simulations of fully developed flows after five wind turbine revolutions over the snapshot data. Our findings show that the inner section of the blades, which is composed of airfoils with larger cross-sections, is responsible for the dominant components of the wake, while the contribution of the wake from the outer section of the blade is significantly lower. Therefore, designing more aerodynamic sections for the blade’s inner section can help reduce the dominant wake components and thus decrease the inter-turbine distance in future wind farms.

Numerical flow field investigation around guide vane of a high head Francis turbine

Guide vanes are the most eroded component of the Francis turbine, and flow instabilities around guide vanes influence the flow field at the runner inlet. Guide vane cascade can be considered an alternative method to investigate the flow field, which maintains flow similarity with the prototype turbine. The objective of this paper is to numerically analyze the flow field around the guide vane cascade. A single guide vane cascade numerical model is developed to perform the simulation using commercial software ANSYS 2022. Two turbulence models, shear stress transport k-ω and standard k-ε, perform steady-state simulation at the best efficiency point. The pressure and velocity distribution are obtained at mid-span, and around the pressure and suction sides of the guide vane. Numerical simulation on a scaled prototype full turbine has also been performed to measure the Francis turbine’s torque and efficiency. The modified Bhilangana- III guide vane profile is installed in the B-III hydropower plant in India and taken as a reference Francis turbine. The velocity and pressure distributions obtained around guide vanes of the scaled full turbine are compared with the velocity and pressure distributions of the single guide vane cascade. A difference of 7.25 % in maximum velocity and 9.40 % in maximum pressure at the mid-span of the guide vane is found between the guide vane cascade and scaled full turbine at the best efficiency point. The overall efficiency of the scaled turbine is also measured, and a difference of 0.83 % between the numerical result and scaled hill chart at the best efficiency point was found.

Operational Expenditure Modelling of the X-Rotor Offshore Wind turbine concept: Sensitivity of Key Modelling Assumptions

The focus of this paper is operational expenditure modelling of the novel X-Rotor offshore wind turbine concept. The X-Rotor presents significant opportunities for operational expenditure reduction. There are, however, numerous uncertainties associated with modelling of those costs. Namely; failure rates for a novel concept are difficult to quantify, and the design of the concept is still being refined. These uncertainties may be addressed via simple sensitivity analyses. Here, three such sensitivity analyses are presented: one focusing on the main bearing failure rate, one on the generator failure rate, and one exploring the provision of redundancy via the operational strategy of secondary rotors. The main bearing failure rate had a particularly significant impact on operations and maintenance costs, accounting for approximately 22% of costs under baseline assumptions. The generator was less impactful as a cost driver, accounting for approximately 10% of costs under baseline assumptions. Lastly, assuming the X-Rotor could operate at 50% capacity upon failure of one of the secondary rotors decreases the operational expenditure by 8% compared to full turbine unavailability.

A Comparative Study of Optimal Individual Pitch Control Methods

Wind turbines are subjected to asymmetric loads and fatigue with subsequent increases in their dimension and capacity, leading to a reduction in their lifetime. To address this problem, the individual pitch control (IPC) technique is quite familiar in the control of wind turbines. IPC is used to reduce the tilt and yaw moments, simultaneously alleviating the turbine blade-root bending moments (BRBMs). This study discusses the performance of model predictive control (MPC), H-infinity (H∞), and proportional and integral (PI)-based IPC strategies integrated with collective pitch control. The performance of the reported controllers has been validated using the National Renewable Energy Laboratory (NREL) 5 MW full nonlinear reference wind turbine. Simulation studies are conducted at varying wind speeds and turbulent intensities as per international electrotechnical commission (IEC) norms. Comparative results in the time and frequency domains indicate that the H∞ based IPC achieves enhanced control performance in terms of reduction in BRBMs and damage equivalent load compared to MPC and PI-based control strategies.

Trade-offs between aggregated and turbine-level representations of hydropower in optimization models

To model a future power system with high shares of variable renewables, it is essential to capture the flexibility of dispatchable technologies such as hydropower. However, the representation of hydropower is often oversimplified in energy system investment models, such that the flexibility of hydropower is significantly exaggerated. This suggests the need for improved representations of hydropower that capture physical river dynamics but are computationally efficient to maintain the tractability of large models. Here, we develop a series of hydropower optimization models for a single river with various levels of techno-physical detail to evaluate options for hydropower representations in energy system investment models. All models operate hourly over a full year with perfect foresight. We explore trade-offs between accuracy and computational time involved in including features such as the river network, head-dependent power production, and discharge-dependent turbine efficiencies. We find that the level of detail significantly affects the optimal production and confirm that a simplistic hydropower representation similar to those often used in investment models significantly overestimates the flexibility of hydropower. The most detailed nonconvex model includes a full river network, head-dependency, and turbine efficiencies and is solved in just one hour on a modern desktop computer. Furthermore, we linearize this detailed model, thereby reducing computation time to one minute while featuring production dynamics substantially more similar to the full nonconvex model than a naive linear network model. These contributions pave the way for improving hydropower representations in investment models to avoid overestimating the flexibility that hydropower may provide.

Beyond 15 MW: A cost of energy perspective on the next generation of drivetrain technologies for offshore wind turbines

Leading wind turbine manufacturers are racing to build larger and more powerful offshore machines. Drivetrain configurations often use a permanent-magnet synchronous generator (PMSG), in either a direct-drive configuration or coupled to a gearbox. With increasing demand for critical rare-earth magnets, new generator technologies are emerging to ensure a stable and secure supply chain. We evaluate three different topologies of radial flux synchronous generators employing high field magnets with reduced or no rare-earth content: a direct-drive interior PMSG (DD-IPMSG), a geared drivetrain combining a medium speed gearbox with a PMSG (MS-PMSG), and a direct-drive low-temperature superconducting generator (DD-LTSG). We develop a conceptual design module for each of these technologies within a larger framework for full turbine design. This provides the fairest comparison between technologies at nominal power ratings from 15–25MW, which represent the next generation of offshore wind turbines. The analyses show that if operational expenditures (OpEx) are constant across the technologies, MS-PMSG results in the lowest LCOE with reductions of up to 7% relative to DD-IPMSG. DD-LTSG also yields lower LCOE values by 2%–3% for fixed-bottom turbines and 3%–5% with a floating platform. However, results are sensitive to OpEx assumptions, with a mere 10% increase causing the conclusions to shift.

ANALYSIS OF THE CONTROL SYSTEM OF A WIND PLANT CONNECTED TO THE AC NETWORK

The dynamics of the development of alternative power sources over the past few decades are presented, which gives reason to talk about the trends in the further development of wind energy. An analysis of the structures and technical characteristics of wind generators is provided, namely, types of electric motors, power circuits of semiconductor converters that provide the generation of electrical energy to the general industrial electrical network. The issue of the possibility of operation of wind generators in wide wind ranges, the issue of emission of reactive power and higher harmonics of currents to the general industrial electrical network, as well as the issue of the efficiency of various structures of wind generators are considered. A wind turbine control system with an asynchronous generator is proposed. A study of transient control processes and energy compatibility of a full energy conversion wind turbine with a power supply network by simulation computer modeling in the Matlab / Simulink software environment is given. The obtained result indicates the possibility of operation of an asynchronous generator with a short-circuited rotor as part of a wind turbine, which makes it possible to provide power to the alternating current network at low wind speeds.

Prediction of aerodynamic performance of NREL offshore 5‐MW baseline wind turbine considering power loss at varying wind speeds

AbstractIn this study, a computational fluid dynamics (CFD) model was developed to simulate the aerodynamic performance of the National Renewable Energy Laboratory (NREL) offshore 5‐MW baseline wind turbine with single rotor and full wind turbine. Using statistical methods, the relation between pitch angle and performance when the speed is above the rated wind speed was analyzed; furthermore, other published data were compiled to establish the functional equations of power, thrust with various inflow wind speeds, and pitch angles. In addition, according to shape optimization based on parametric modeling, the two‐dimensional cross‐section of the wind turbine blade can be defined through a metasurface approach, and the three‐dimensional surface modeling of the wind turbine blade, nacelle, and tower is completed using the nonuniform rational B‐splines (NURBS) interpolator. In terms of aerodynamic simulation, the unstructured polygon mesh was used herein to discretize the space and simulate the highly curved and twisted surfaces of the blade. In this study, the compact and accurate mesh form obtained through a grid independence test will be used to analyze the distribution of the pressure coefficient, shear stress coefficient, and limited streamline on the blade surface at various inflow wind speeds and pitch angles to understand the differences between different turbulence models and the causes of power and thrust attenuation at high inflow wind speeds. In addition, the phenomena of blade‐tip vortices, dynamic stall, blade loading, and the interaction between nacelle and tower were collectively explored.

Using Machine Learning for Loss Prediction in a Hybrid Meanline Modeling Method to Deliver Improved Radial Turbine Performance Prediction

Abstract Low fidelity modeling approaches remain attractive due to an unrivaled ability to predict full turbine performance maps quickly compared to high-fidelity approaches such as computational fluid dynamics (CFD), especially in the preliminary design process. As improvements in performance on a component level approach a point of diminishing returns, the ability to efficiently optimize the complete charging system for a given duty is a topic attracting significant research interest. In the case of turbocharging applications, existing engine and powertrain simulations require turbine maps to calculate the turbine performance, which are usually obtained from experimental testing. Unfortunately, the need for extrapolation is unavoidable because of the limited range of testing data available, leading to inaccuracies especially at off-design conditions. To enable intensive modeling and optimization of complete vehicle powertrains for different drive cycles, the current piece of work seeks to combine the advantages of machine learning techniques and physical meanline modeling to facilitate faster, more accurate predictions of complete turbocharger maps. This paper presents a novel methodology for turbocharger turbine rotor and nozzle performance prediction based on hybrid modeling. The turbine rotor and nozzle were parameterized to conduct CFD simulations for a wide variety of turbine geometries, which were used to form a database to train an artificial neural network (ANN). The predicted losses provided by the ANN were then utilized in the meanline code, substituting for the conventional empirical loss models. As well as removing the need for empirical loss models, modifications were undertaken to the meanline approach to further enhance modeling accuracy. First, in order to accurately characterize the stage mass flow capacity, the losses occurring in the nozzle and rotor were subdivided into those occurring before and after the throat. A second novel aspect is that the aerodynamic blockage level at the rotor throat was implemented as a variable rather than a constant value. By training the ANN to predict the variation of blockage with geometry and operating condition, a more accurate depiction of the changing secondary flow fields could be achieved. The capabilities of the hybrid meanline modeling method were evaluated on several unseen test cases. The resulting predictions of efficiency and mass flowrate demonstrated strong correlation with CFD results and experimental test results. The hybrid meanline modeling method therefore displays great potential in wide range radial turbine performance prediction with enhanced accuracy in comparison to traditional approaches.

HCF and LCF Analysis of a Generic Full Admission Turbine Blade

A numerical turbine-blade fatigue-life analysis method is suggested. This method comprises a stationary thermal 3D finite element (FE) analysis of the hot run for the combined high-cycle fatigue (HCF) and creep analysis, and a follow-on (one-way coupled) quasi-stationary structural 3D FE analysis (including six load steps) of a single and two half turbine blades and the related disk and rotor section and a (modified Goodman equation based) post-processing fatigue life analysis for the highest HCF-loaded point of the turbine blade. For the low-cycle fatigue (LCF) analysis, this includes a transient thermal 3D FE analysis of two full loading cycles, a follow-on (one-way coupled) quasi-stationary structural 3D finite element analysis of a single and two half turbine blades and the related disk and rotor section and a (modified-Langer-equation-based) post-processing fatigue life analysis approach for the highest LCF-loaded point of the turbine blade. Finally, this approach is demonstrated by the numerical HCF, LCF and creep analysis of a generic turbine blade of the first rotor row of a full admission hydrogen turbo pump of a 1 MN thrust class gas generator LOX-LH2 liquid rocket engine (LRE). For this numerical example, the LCF loading turned out to be dominant. Creep turned out to be negligible.

Experimental and two-scale numerical studies on the behavior of prestressed concrete-steel hybrid wind turbine tower models

Prestressed concrete-steel hybrid (PCSH) wind turbine tower has been recognized as an efficient alternative to traditional steel tube supporting towers for wind farms in harsh sites such as mountain regions. To investigate the global and local mechanical behavior including failure patterns of a full scale PCSH wind turbine towers, an experimental study on a substructure of a scaled PCSH tower is carried out firstly. Then, a material subroutine for three-dimensional (3D) fiber beam elements suitable for implicit analysis on the mechanical behavior of the substructure of the scaled PCSH tower is developed. A two-scale numerical model of the substructure of the scaled PCSH wind turbine tower employing the developed 3D fiber beam elements and solid elements is developed. The accuracy and efficiency of the developed two-scale numerical model for the behavior simulation of the substructure of the scaled PCSH wind turbine tower is illustrated by comparing the numerical results with the experimental measurements. Additional comparison of the simulation results using the developed two-scale numerical model is made with them of a model using sole 3D fiber beam elements and a model using sole solid elements, respectively. Results show that the force–displacement curve determined with the developed two-scale model is close to the test result and coincident well with that of the two models using 3D fiber beam elements and the solid elements. The developed two-scale model can describe the global behavior, the local failure patterns and the stress distribution of the tested specimen accurately with improved simulation efficiency. Finally, the validated two-scale modelling approach is employed to analyze the static behavior, modal parameter, and fatigue of the optimized full-scale PCSH wind turbine tower previously developed by the authors. The simulation results show that the two-scale model can reflect the stress of the PCSH wind turbine tower at the critical position as well as the global mechanical behavior with higher computational efficiency. The fiber beam model can be used for predicting only global, but not local, behavior.

An optimal strategy for application of photovoltaic-wind turbine with PEMEC-PEMFC hydrogen storage system based on techno-economic, environmental, and availability indicators

In this study, a hybrid system for power generation for an off-grid application is studied. The power generators of this system are photovoltaic (PV) solar modules and wind turbines, while the combination of polymer electrolyte membrane electrolyzer and fuel cell (PEMEC and PEMFC) is used for energy storage. Energy, environmental, and economic (3E) aspects are taken into consideration, whilst the availability analysis is also done to achieve a better insight. Number of PV modules is selected as the decision variable, and it is determined through a dynamic multi-objective optimization with objective functions from the aforementioned aspects. The optimized hybrid system is compared with full PV and full wind turbine electricity production scenarios. The studied hybrid system is found to be 27.72% and 46.92% better in terms of payback time, respectively, compared to the solar or wind system alone. Moreover, the hybrid system has been shown to be more efficient than the other two systems, with an availability of 97.70%. The levelized cost of electricity (LCOE) for the studied hybrid system is 0.2475 $.(kWh)−1, as well. It has also the potential of saving 86940.2 kg of CO2 during a year, which is 11.65 and 19.51% higher than only PV and only wind turbine conditions, respectively.