Turbine Performance Research Articles

Aerodynamic and Structural Assessment of Floating Wind Turbine Rotor Under Varying Tilt Angle

Predicting the aerodynamic performance of floating offshore wind turbines (FOWTs) proves challenging due to platform motion induced by waves. The effect of wind and waves results in a six-degree-of-freedom motion of the platform, directly influencing turbine performance. Understanding the impact of specific degrees of freedom (DOF) motions on aerodynamics and structural response is crucial for effective wind turbine design. This research examines the impact of rotor tilt on both aerodynamic performance and structural response. The investigation employs computational fluid dynamics (CFD) analysis and mapping aerodynamic loads onto the finite element (FE) mesh for structural analysis. The study employs a comprehensive 3D simulation, utilizing the moving reference frame (MRF) method for the NREL 5 MW reference wind turbine CFD simulations. It explores different rotor tilt angles (5°, 10°, 15°, and 20°) encountered by offshore structures during their operation and examines their impact on aerodynamic performance. Predicted aerodynamic loads were mapped onto the blade FE mesh using the radial basis function (RBF) interpolation technique and solved using the open-source FE solver CalculiX. The analysis shows that the turbine performance is relatively unaffected up to a tilt angle of 10°. However, further increase in rotor tilt angle adversely impacts turbine performance, leading to notable reductions in thrust and power output. The fluid-structure coupled analysis provided insights into the deformations and stresses experienced by the turbine blade, indicating a notable increase in flap-wise displacement for larger tilt angles, while edge-wise displacement is not as significantly affected. The maximum stress location on the blade generally correlates well with actual observations.

Effect of uneven inflow on hydrodynamic performance of bulb turbine

Abstract Bulb turbine unit is characterized by its low head, large discharge, and short flow passage. The guiding wall separating the power house section from the flood discharge section may cause uneven inflow before its neighbor units when the power house section is located off the river’s mainstream. In this study, selecting a bulb turbine hydropower station in China as the subject, we establish a three-dimensional CFD model that contains the full flow passage of the turbine unit and partial upstream reservoir, to analyze the effects of uneven inflow on the hydrodynamic performance of the bulb turbine. The results show that under this power station layout, flow separation occurs on the left side of the guiding wall, resulting in a low pressure zone and causing the flow in a three-dimensional vortical pattern. The low pressure and flow energy loss lead to the reduction of the neighbor units’ head, causing the discharge decreasing, and the output cannot reach the expectations. This situation can be improved by shortening the guiding wall, indicating that the unit’s performance is strongly related to the hydraulic structure arrangement. The results can provide some references for the design and operation of the related project.

A comprehensive investigation on Darrieus vertical axis wind turbine performance and self-starting capability improvement by implementing a novel semi-directional airfoil guide vane and rotor solidity

Darrieus vertical axis wind turbine is classified as a lift-based power generation turbomachine. However, it is burdened with the limitations of mid-range efficiency and requiring initial torque for startup. The quest to improve the turbine's performance has focused on enhancing its aerodynamic performance and self-starting ability. One of the most effective approaches is to flow control and injection toward the rotor blades. This computational fluid dynamics research study utilizes a novel geometry known as the “Semi-Directional Airfoil Guide Vane” (SDAGV) to inject airflow smoothly and effectively toward the rotor blades at the upstream section. The investigation found that using a two-passage SDAGV increased rotor efficiency by up to 55% at a tip speed ratio (TSR) of 2.5. The pressure distribution analysis showed that azimuth angles between 90° and 135° significantly impacted the rotor's self-starting ability. Additionally, studying the turbine solidity revealed that a five-bladed rotor with SDAGV had a higher self-starting capability and efficiency than a two-bladed rotor with SDAGV. This was because its power coefficient (Cp) was approximately 160% greater at TSR = 1.4. Due to blade-to-blade interaction, high-solidity turbines from TSR = 2 onwards face performance challenges, which means their efficiency drops in the low-TSR range.

Computational investigation of the effect of the trailing edge thickness on the wind turbine performance

Trailing edge (TE) thickness is a manufacturing constraint in blade design, especially for airfoils with a sharp TE. To achieve a specific TE thickness, blade geometry is often modified during the design process, typically in the outer zone of the blade where the airfoil’s TE is thinner. This area has a significant impact on energy production and loads. Quantifying the effect of TE thickness modifications is crucial for making informed design decisions.Therefore, this study quantifies and compares the impact of linear and polynomial geometry modifications on airfoil aerodynamics and turbine performance. Xfoil and OpenFAST were used to calculate these performance variations in the well-known NREL 5 MW wind turbine. The TE thickness of the model was modified to meet various manufacturing constraints, ranging from no restriction to a limit of 12mm TE thickness.In terms of the aerodynamic behavior of the airfoils, the maximum efficiency of airfoils with low relative thickness decreases as the TE thickness increases. Annual Energy Production shows a reduction of up to 0.42% for the worst case, while blade root loads increase by up to 20%. For low relative thickness airfoils, the linear method has proven to be a better option with less impact on performance.

Dragonfly-Inspired Blades for high Aerodynamic Performance small Horizontal Axis Wind Turbine

Inspired from the fascinating realm of Dragonfly features, this study intricately investigates the aerodynamic performance of a distinctive 1 m diameter small-scale Horizontal Axis Wind Turbine characterized by a unique bio-inspired tandem-blades configuration. Based on experimental wind tunnel tests and computational fluid dynamics simulations, the turbine performance is explored at different Tip Speed Ratios (TSRs). Remarkably, the bio-inspired turbine exhibits exceptional traits, achieving a notable peak power coefficient of approximately 0.35 at a low TSR of 3. A detailed investigation includes thorough analyses of pressure contours, relative velocity distributions, and individual blade contributions, revealing unique dynamics within the tandem configuration. The fore blade notably prevails in extracting wind energy, showcasing superior performance. While the hind blade influence in enhancing the fore blade efficiency emerges, underscoring the role of blade interactions in this bio-inspired designs. This study contributes significantly to the comprehension of the new design dragonfly-inspired wind turbine aerodynamics.

Impact of dynamic stall model tailoring on wind turbine loads and performance prediction

The future of wind turbines will be characterised by long, slender blades subject to dynamic inflow and aeroelastic deflections. This makes the next generation of blades more prone to encounter dynamic stall effects, in which significant forces and loads fluctuations can be expected. Dynamic stall models can be tailored to suit the aerodynamics of different airfoils. Although different dynamic stall models exist, the impact of the choice of model, its implementation and calibration on the overall wind turbine performance remains to be assessed. In this work, we gathered an experimental dynamic dataset for a representative airfoil, the FFA-W3-211, to define the semi-empirical time constants for the Beddoes-Leishman dynamic stall model. An important differentiation is made between stall regions for positive and negative angles of attack, and the impact of tailored coefficients is assessed at airfoil scale. The difference between the tailored and untailored model is quantified for power performance and loads of the IEA 15 MW reference wind turbine. The results highlight a significant load over-prediction from the untailored Beddoes-Leishman model, whereas changes in power performance are negligible.

Sensitivity of the Prediction of Wind Turbine Wakes to the Sub-Grid Scale Model

In a large-eddy simulation (LES) approach, the sub-grid scale (SGS) model accounts for the contribution of eddies and their fluxes whose length scales are smaller than the filter width. In wind turbine and farm simulations, different SGS models have been adopted, but their impact on turbine performance and wake prediction remains unknown for non-neutrally stable atmospheric boundary layers. Here, large-eddy simulations of an NREL–5MW wind turbine in stable atmospheric conditions are performed with six SGS models: standard Smagorinsky, Lagrangian-Averaged Scale-Dependent Dynamic (LASDD), Wall-Adapting Local Eddy-Viscosity, Turbulent Kinetic Energy, Stability Dependent Smagorinsky, and Anisotropic Minimum-Dissipation (AMD) models. The resolved flow field and turbine loading have shown limited sensitivity to the SGS model with some deviations from the LASDD in wind speed and turbulence intensity at the turbine elevation. This limited sensitivity is owed to the adopted high-resolution grid necessary to provide an acceptable resolution for the actuator-line method. Regarding the computational costs, the LASDD model has the highest compute overhead to the LES compared to the other five SGS models. The AMD model is simple to implement and provides three-dimensional variation of the SGS eddy-viscosity without any parameter tuning, thus it has the highest potential to be used in LES of wind turbines and farms operating in stable conditions.

Performance improvement of a Vestas V52 850kW wind turbine by retrofitting passive flow control devices

This study presents the results of a collaborative effort between academia and industry aimed at further enhancing the benefits provided by Vortex Generators and Gurney Flaps. To achieve this objective, an integrated approach was employed, involving wind tunnel experiments, on-site measurements, and computational simulations to design devices tailored for an onshore (Vestas V52, 850 kW) turbine and assess their influence on turbine performance. Device selection was based on wind tunnel measurements, while their positioning on the blade was based on infrared thermography images from the field. A Reynolds Averaged Navier Stokes solver was used to predict the performance of the devices on both airfoil and blade level. The final assessment of the upgrade pack was based on SCADA data and Lidar measurements. The results show that an Annual Energy Production uplift of 5.77% is measured for this turbine.

Multiscale-simulation method for the wear behaviour of planetary journal bearings in wind turbine gearboxes

Wind energy is one of the most important renewable energy sources. To maintain competitiveness wind energy needs to be cost effective. Increasing the performance of wind turbines can help to reduce the total cost of wind energy. The power output can be increased by an increase in turbine rotor size since the power increases disproportionately with the rotor diameter. The increase in rotor size inherently comes with an increase in overall wind turbine size to cope with the increasing loads. Since the nacelle weight cannot be increased without limitation, e.g. due to the effect on the tower and costs, an increase in power density is necessary. The usage of journal bearings instead of rolling bearings for the application in planetary gearboxes in wind turbines is one way to increase the power density and reliability of the drivetrain. When designed and operated correctly, journal bearings have a longer service lifetime than rolling bearings. Wear simulations aid in the design of journal bearings. This work presents a simulation method for the wear prediction of planetary journal bearings in wind turbine gearboxes. The method is validated with measurements on a component test rig. The transfer to the wind turbine gearbox is shown by means of simulation.

Assessment of wind energy resource in the western region of Somaliland

As the population of Somaliland continues to grow rapidly, the demand for electricity is anticipated to rise exponentially over the next few decades. The provision of reliable and cost-effective electricity service is at the core of the economic and social development of Somaliland. Wind energy might offer a sustainable solution to the exceptionally high electricity prices. In this study, a techno-economic assessment of the wind energy potential in some parts of the western region of Somaliland is performed. Measured data of wind speed and wind direction for three sites around the capital city of Hargeisa are utilized to characterize the resource using Weibull distribution functions. Technical and economic performances of several commercial wind turbines are examined. Out of the three sites, Xumba Weyne stands out as the most favorable site for wind energy harnessing with average annual power and energy densities at 80 m hub height of 317 kW/m2 and 2782 kWh/m2, respectively. Wind turbines installed in Xumba Weyne yielded the lowest levelized cost of electricity (LCOE) of not more than 0.07 $/kWh, shortest payback times (i.e., less than 7.2 years) with minimum return on investment (ROI) of approximately 150%.

Numerical investigation of the vortical structures in the near wake of a model wind turbine

It is well known that the vortex system in a horizontal axis wind turbine wake is highly relevant in terms of fatigue loads and performance of wind turbines located in the wake of other wind turbines. The breakdown process of tip vortices particularly influences the mixing process of the low-speed wake region with the undisturbed flow outside the wake. As a collaboration with the Technische Universität Berlin (TUB), a major goal in a joint research is to study the effects involved in tip vortex breakdown. TUB designed a model turbine that will be towed through a large water tank to analyse and to control the tip vortex decay. To accommodate the measurement equipment, the ratio of blade length to nacelle length is unconventionally small, leading to uncertainty regarding the effect on the breakdown of the tip vortex. Due to the dimensions of the model wind turbine the root vortex system and the nacelle wake are not comparable to former studies and should therefore be investigated in detail. To do so computational fluid dynamics, in particular delayed detached eddy simulations, are conducted for the model turbine with the compressible flow solver FLOWer and the two-equation Menter-SST turbulence model. Two simulations are conducted with and without the nacelle. The results indicate that the root vortices propagate downstream and interact with each other. Additionally, these vortical structures are also influenced by the geometry of the turbine nacelle which causes faster decay of the root vortices compared to a configuration without the nacelle. However, the root vortex breakdown does not influence the tip vortices as the turbulent intensity matches for the area where tip vortices are present. In short, this investigation shows that the influence of the nacelle geometry and root vortex system on the tip vortices is negligible. Thus, the model wind turbine designed by TUB is suitable for the investigation of tip vortices.

The impact of blockage and wakes on seven power performance tests conducted at two wind farms

Blockage and wakes can potentially influence wind turbine power performance measurements (PPM), distorting the measured power curve relative to the true performance of the test turbine. In this study, we take a previously proposed method to correct for the impact of blockage and wakes and test it on seven PPM conducted in simple terrain at two wind farms. Each PPM was completed according to the prevailing standard from the International Electrotechnical Commission. The correction factors derive from Reynolds-Averaged Navier-Stokes simulations of the two wind farms, and we apply these factors to the measured wind speed data on a record-by-record basis. The wind speed corrections clearly reduce variability in the measured power coefficients for the three PPM affected by long-distance wakes. The corrections do not reduce performance variability within the other four PPM. They also do not reduce differences in measured performance between the turbines at each wind farm, though numerical site calibrations do. Given these results, and considering uncertainty in the measurements, including confounding influences like terrain and turbine differences, validation against many more PPM is likely needed to adequately assess the reliability and utility of the correction method.

Effects of a Near Wake model on the performance of a Multi-Megawatt wind turbine with an active flap

The impact of including the near wake model in the aeroelastic models of an SWT-DD-120 wind turbine equipped with an active trailing edge flap system (ATEF) is studied. The ATEF installed on this turbine was tested in full scale in a series of campaigns between 2018 and 2022. Since standard BEM methods cannot accurately capture the induced velocities near the transition areas of the start and end of flap add-ons due to the strong interaction of the local trailed vorticity with the neighboring blade sections, this study aims to investigate if and how the near wake model is relevant in the aerodynamic and aeroelastic characterization of rotor blades with active flaps. It is shown that the Near Wake model, when combined with an active trailing edge flap system, has a marginal impact on the blades’ thrust-related loads, independently from the presence, actuation state, and actuation frequency of the flap. The impact on the torque-related loads is also marginal at the blade root, while it becomes more relevant in the blade area where the flaps are deployed.

Numerical study on the influence of the bucket offset angle on the flow field of Pelton turbines with six-nozzles

Abstract Pelton turbines are emerging as a primary means for exploiting ultra-high water head resources. The hydraulic performance of a Pelton turbine is determined by the design of its runner/bucket. Among the critical parameters that affect the hydraulic performance of multi-nozzle Pelton turbines is the bucket offset angle (α). To investigate the influence of bucket offset angle on the flow field of Pelton turbines with six nozzles, this study conducted unsteady numerical simulations of gas-liquid two-phase flow for various bucket offset angles, employing the VOF multiphase model combined with the SST k-ω turbulence model. The results reveal that as the bucket offset angle increases, the axial width of the water sheet formed by the current jet progressively widens, with a tendency to catch up with the water film formed by the previous jet during the torque rising stage. Moreover, the increased bucket offset angle causes the water sheet to distribute more closely to the bucket cutout, raising the risk of leakage from the cutout. Notably, at α= 10°, some of the water sheet has already flowed out of the cutout and collided with the subsequent jet.

Estimating the performance of wind turbines misaligned with respect to the wind direction using a simplified CFD based approach

Wind direction in atmospheric boundary layer changes constantly. As such, the power extracted from the wind turbines in a wind farm is subjected to change. This change in wind direction impacts the wake pattern which in turn affects the power output of the downstream wind turbines. Empirical wind farm models are useful in such cases to assess the overall performance of the wind farms. However, the results provided by these models can be made more useful if fluid-structure interaction (FSI) effects are also considered. In the present work, we begin by looking at the potential flow model and the issues associated with it and used a modified model with constant vorticity to analyze the wind power available to the downstream wind turbines in a wind farm misaligned with respect to wind direction for irrotational flow. A simplified FSI based approach is used to carry out the simulations without the need of modelling the complicated wind turbine geometry.

Research on Automatic Testing of Pump Turbine Model Test Based on Intelligent Technology

Abstract In order to test the performance of pump turbine, it is necessary to collect and analyze the performance indexes such as energy characteristics, stability performance, cavitation performance and force characteristics of the unit through the pump turbine model test test system. however, the current test systems all use manual operation based on the standard specification requirements to handle the data collection and analysis of the test, and the accuracy of the data relies on human experience and the efficiency is not high. The method described in this paper uses emerging computer test technology means such as big data technology, noise and image recognition technology to automatically and efficiently complete the test data test, and quickly complete the test test, while the test results are more accurate.

Effect of Shroud Components on the Performance of a Small Horizontal Axis Wind Turbine

Effect of Shroud Components on the Performance of a Small Horizontal Axis Wind Turbine

Analytical Simulation Approach to Evaluate the Ambient Humidity Effects on the Performance of a Wind Accelerator

Abstract The power production of wind turbines is experiencing an upward trend. However, on the other hand, the wind turbine’s performance slows down due to unseen changes in the environment. Humidity is one of the environmental factors affecting the performance of wind turbines. When humidity levels are high in the atmosphere, air is less dense. This air is lighter, and it results in reduced air pressure. A remedy to increase the air pressure in the direction of wind flow is to locate a wind accelerator, an aerodynamic device before the wind turbine to amplify the incoming wind speed and reduce the impact of humidity on the wind energy. This study intends to investigate the impact of environmental humidity on the performance of the wind accelerator. The study includes modelling the wind accelerator using Ansys 2023R1, to simulate different humidity levels. An analytical simulation is conducted to describe the aerodynamic behaviour of the wind accelerator in response to the changes in ambient humidity. The air at different percentage levels of humidity is passed through the proposed wind accelerator geometry to observe the wind speed variation and kinetic energy of the wind. The simulation study reveals that the wind speed and kinetic energy show higher values when the humidity is at a lower level, while the opposite is true when the humidity is higher. This emphasizes how important it is to consider all environmental elements while designing and developing wind turbines and wind accelerators for optimal performance subjected to various climatic conditions.

Study on the Influence of Protuberance Amplitude on the Performance of Vertical Axis Wind Turbines

Abstract The performance of vertical axis wind turbine (VAWT) is mainly affected by the dynamic stall process of the blade. Inspired by the anti-stall performance of the humpback whale flipper, leading edge protuberances (LEPs) are applied to 2-blade VAWT. Based on computational fluid dynamics simulation method, the effects of LEPs amplitude on VAWT performance are investigated when blade tip speed ratio is 2.19. The results show that the larger the amplitude of the LEP, the lower the average power coefficient. When the number of protuberances is 3, the average power coefficient of the VAWT with a protuberance amplitude of 6.625mm is 1.8% higher than prototype blade. Considering the impact of increasing the chord length of biomimetic blades, the average tangential force coefficient of all biomimetic VAWTs decreases. The peak section performance of the bionic blade decreases significantly while the trough section performance increases significantly. The difference between the peak section and trough section of the LEPS plays an important role in improving the performance. This study provides a reference for the application of bionic protuberances in VAWTs.

Research on incipient and critical cavitation of a Francis turbine

Abstract Cavitation is an important performance index to evaluate the comprehensive performance of hydraulic turbine. Determination of the plant cavitation coefficient is one of the most important tasks in the design phase of a hydro-power station. In order to improve the design rationality of the cavitation coefficient, numerical simulations of a Francis turbine were carried out to study the cavitation evolution characteristics. A detailed comparative analysis were made to clarify the different cavitation coefficients and impacts on the Francis turbine. Discussions on plant cavitation coefficient selection of hydro-power plant were made form the perspective of cavitation influence on the unit. Based on these investigations, it can be concluded that a certain safety margin of incipient and critical cavitation coefficient were needed considering the rapid efficiency drop near the critical cavitation and serious pressure pulsation near the incipient cavitation condition. The ratio between the plant cavitation coefficient and critical cavitation of the studied Francis turbine were larger than the current standard in China, which means the good cavitation performance of the unit after it put into operation. This study can provide a reference for determining the cavitation coefficient more accurately and ensuring the operation safety of the unit.