Rotor Performance Research Articles

Experimental and three-dimensional performance analysis of a bio-inspired fish-ridge vertical axis wind rotor

The savonius vertical axis wind rotor has a simple structure, making it a suitable choice for power generation in small-scale, low wind speed environments. However, its wind energy conversion efficiency is low. To improve the conversion efficiency of the wind rotor using the proposed fish-bridge structure, the wind tunnel tests are conducted to collect actual wind and rotational speeds. In addition, Computational Fluid Dynamics (CFD) simulation is conducted to reveal potential operating mechanisms, with special emphasis on analyzing the effects of aspect ratio and end plate on the performance of the fish-ridge wind rotor. The CFD results show that the wind power coefficient of this wind rotor presents an increasing trend with the increase of the aspect ratio and the area of the end plate, and that with round end plates is improved by 24.26 % compared to that of the wind rotor without end plates, and that with an aspect ratio of 3.5 is improved by 32.58 % compared to that of the wind rotor with an aspect ratio of 1. By increasing the aspect ratio and the end plate area of the wind rotor, the contact airflow is raised and concentrated, which improves the aerodynamic performance of the wind rotor.

Numerical and experimental study on the critical geometric variation based on sensitivity analysis on a compressor rotor

Abstract Different types of geometric variations often appear coupledly in manufactured blades. It is desired to identify the ones that have the strongest impact on the performance. In this paper, the influence of multiple geometric variations on the compressor rotor blade at the design point is studied. Two hundred and nine varied blades are constructed by adding variation data to the design-intent blade and assessed using steady-state Reynolds-Averaged Navier–Stokes (RANS) simulations. It is shown that the region near the lower and upper end of the blade is more sensitive to geometric variations. Spearman’s rank correlation coefficient is used to measure the sensitivity of rotor performance to geometric variations. The results show that the stagger angle variation is the most influencing variation. Local sensitivity analysis at different spans also shows that the stagger angle variation is an important geometric variation that needs more attention during blade manufacturing. Also, the influence of geometric variations can reach further than nearby regions. Consequently, experiments on linear cascades at different spans of the rotor are carried out to study the effect of stagger angle on flow characteristics. Results show that the stagger angle variation could lead to different changes in performance depending on the specific cascade profile.

Numerical and experimental investigation for helical savonius rotor performance improvement using novel blade shapes

Wind energy is extensively invested as a renewable and clean energy source. Savonius wind rotor, as an energy converter, has the merit of being appropriate for specific applications. The current paper centers on the performance enhancement of a helical Savonius wind rotor through the blade shape modification. The basic objective is to assess and compare, numerically and experimentally, the performance of two rotors with novel blade shapes named delta bladed and two-stage delta bladed shapes in relation to a helical Savonius rotor. Numerical study was conducted using Ansys Fluent software. 3-D unsteady simulations were carried out through the use of the SST k-ω turbulence model based on the finite volume method solver. Aerodynamic flow and performance characteristics were investigated. Static and dynamic experimental tests were undertaken on a wind tunnel. An improvement in Cp by 22.58 % and 29.5 % for the two-stage delta bladed rotor and 19.35 % and 16.4 % for the delta bladed rotor over the helical Savonius rotor was recorded, respectively, numerically and experimentally. In addition, the self-starting ability as well as the aerodynamic flow characteristics of the helical rotor were enhanced with the novel blade shapes.

An rVPM-Based Aerodynamic Hybrid Optimization Method for Coaxial Rotor with Differentiated Upper and Lower Blades in Both Hover and High-Speed Cruising States

To enhance the performance of rigid coaxial rotors across both hovering and high-speed cruising conditions, this study develops a novel aerodynamic optimization method that differentiates between the upper and lower rotors. Utilizing the lifting line and reformulated viscous vortex particle method (rVPM), this approach models the complex wake fields of coaxial rotors and accurately assesses the aerodynamic loads on the blades. The optimization of geometric properties such as planform configuration and nonlinear twist is conducted through an innovative solver that integrates simulated annealing with the Nelder–Mead algorithm, ensuring both rapid and comprehensive optimization results. Comparative analyses demonstrate that these tailored geometric adjustments significantly enhance efficiency in both operational states, surpassing traditional methods. This research provides a strategic framework for addressing the varied aerodynamic challenges presented by different flight states in coaxial rotor design.

Experimental Study on Performance of a Wave Energy Converter Rotor with a Moving Platform

A series of experiments were carried out to investigate the performance of a WEC rotor with platform motion. To achieve platform motion, a forced motion device with a rotor was installed in the Ocean Engineering Basin. In this study, the rotor’s performance was examined at various phase stages between incoming waves at three wave heights, and compared to a rotor without a PTO system. The phase stage where the rotor exhibited the largest pitch motion was identified, and the efficiencies of the rotor with the PTO system were analyzed during this stage. Without the PTO system, the rotor experienced its largest pitch motion when the rotating center was positioned at the zero-up crossing point of the incoming waves at three different wave heights. Furthermore, it was observed that in the optimal phase, the rotor’s efficiency increased with relatively large platform motion. These findings provide fundamental data for rotor design.

Evaluation of a Savonius wind turbine in the vicinity of a circular cross-sectional building

Today's urban areas are filled with tall buildings that require significant energy. To enable the implementation of small-scale wind turbines for dispersed electricity generation in cities, it is crucial to evaluate their performance in close proximity to buildings. This study aims to assess the performance of conventional Savonius rotors near a circular cross-sectional building for the first time. The performance of a Savonius wind rotor is being studied at different installation angles (30°, 45°, 60°, and 90°) with a constant non-dimensional gap space (S/D) of 2.0 between the rotor center and building envelope under a constant free-wind speed of 6 m/s. Two possible wind rotor rotation scenarios, inward and outward, are thoroughly tested and studied. Computations are carried out for tip speed ratios (TSR) of 0.4, 0.8, and 1.2. The obtained results are successfully validated for both the Savonius rotor in the free-wind flow (without a building) and a circular cross-sectional building (without a wind rotor) as well. The results show that installing a Savonius rotor at angles of 60° and 90° provides the maximum power coefficient based on the TSR. In contrast, placing the rotor at 30° reduces its performance even more than the reference case. For optimal rotor angles, inward rotation is preferred over outward rotation regardless of the TSR. Finally, there are improvements of 208.72 %–439.95 % compared to the reference case for 60° and 90° under inward rotation.

Rotor Performance and Wake Interaction of Controlled Dual Surging FOWT Rotors in Tandem

Using Large Eddy Simulation (LES) with Actuator Line Model (ALM), this work investigates the system of two surging wind turbine rotors operating under realistic turbulent inflow conditions (TI = 5.3%). The two rotors are placed in tandem with a spacing of 5D and the surging motions are harmonic. A widely used torque controlling strategy, MPPT (Maximum Power Point Tracking), is implemented to ensure a maximium power extraction under all conditions. The rotor performances as well as the field data are surveyed to examine the effectiveness and impacts of the controller. It is found that the power performances of the surging rotors are benefited by the controller with a small margin (∼ 1%) when the surging motions are moderate. The results also show that the controller reacts much slower than the considered surging frequency, making the power performances of the rotors worse than the quasi-steady predictions (targeted values) and complicating the system dynamics. In general, the implementation of the controller has minor impacts on the wake characteristics; however, the strengths of Surging Induced Periodic Coherent Structures (SIPCS) are found to be enhanced.

Aeroelastic analysis of a very large wind turbine in various atmospheric stability conditions

With the growing trend towards larger wind turbine rotor diameters, the impact of wind shear on rotor performance and loads becomes increasingly significant. Atmospheric stability strongly influences wind shear, leading to higher wind shear under stable atmospheric conditions. In this study, the aeroelastic performance of the IEA 22 MW rotor is assessed under inflow conditions generated by different methods. Inflow conditions were generated using turbulence models specified in the IEC Standards and also by Large Eddy simulations. Standalone OpenFAST simulations were conducted with the respective inflow conditions.It was found that at rated and above-rated wind speeds, the time-averaged wind turbine design loads were higher in stable atmospheric conditions, in comparison to the IEC NTM inflow conditions, while the opposite held for below-rated wind speeds. Specifically, the time-averaged root flapwise bending moment and rotor thrust were found to be higher by up to 7% in stable atmospheres. However, maximum design and fatigue loads were considerably higher in the IEC NTM case due to elevated turbulence levels. Compared to the IEC NTM case, the damage equivalent root flapwise bending moment was found to be 30% to 70% lower in the different scenarios.

Uncertainty Quantification Analysis in the Blade Element Momentum Method

The blade element momentum (BEM) method is a widely used non-linear model for the efficient performance evaluation and design of wind turbines. The aim of this paper is to quantify the uncertainty related to BEM model inputs and sub-models, and investigate how these propagate through the model. Uncertainties related to viscous dissipation in the wake, aerofoil force coefficients, and tip-loss models are considered. Global sensitivity to these parameters is analysed using non-intrusive polynomial chaos expansion, which provides a structured method for uncertainty propagation and sensitivity quantification. Sobol indices are employed to rank the relative importance of each factor to the overall uncertainty in the system. By analysing the NREL 5 MW and DTU 10 MW reference wind turbines, we observe that the different rotors may exhibit different levels of sensitivity to input parameters. The effect of viscous mixing in the turbine wake is found to have a significant impact on predicted rotor performance. Uncertainty in tip-loss model coefficients is also found to generally be important, particularly when evaluating spanwise variations in rotor loads. Uncertainty quantification has the potential to improve understanding of BEM modelling, and provide guidance on the importance of sub-model improvements.

Aerodynamic Characterization of the IEA 15 MW Reference Wind Turbine by Code-to-Code Comparison

The consistency of different aerodynamic formulations applied to the analysis of a modern multi-megawatt horizontal axis wind turbine rotor is investigated. The proposed code-to-code comparison involves specific implementations of a hierarchy of solvers based on Blade Element Momentum Theory (AEOLIAN), Actuator Line Modelling (OpenFOAM), free-wake Panel Method (FUNAERO) and blade-resolved Computational Fluid Dynamics (OpenFOAM ). The analysis addresses local and integral aeroloads and flow physical quantities concerning the state-of-the-art IEA 15 MW reference wind turbine in axial uniform flow conditions. The proposed solvers predict consistent rotor performance and blade aeroloads (also in line with data from of IEA Task 47). However, differences emerge close to blade root, where blade-resolved CFD reveals a significant flow separation on the suction side. Furthermore, scattering of induction factors computations is observed, especially in the axial direction. Different methodologies and numerical setup used in blade-resolved simulations allow achieving physically-consistent induction values, especially at blade tip. Finally, flow-field predictions by Computational Fluid Dynamics (CFD) and Panel Method are consistent upstream and close to the disk downstream (except where significant flow separation occurs), whilst a more detailed study on the effect of extending wake refinement zone in CFD simulation is advisable.

Effect of Induction and Blade Elasticity Modelling on Wind Turbine Rotor Performance Predictions

This study investigates the impact of blade induction modelling on the accuracy of wind turbine rotor aeroelastic predictions. It extends the capabilities of AEOLIAN (AErOeLastic sImulAtioN), a Fluid Structure Interaction (FSI) solver based on Blade Element Momentum Theory (BEMT) coupled with a Lumped Mass approach to represent the blade structure. Herein, AEOLIAN’s analytical wake induction engineering model is replaced with the outcomes of a physically-consistent three-dimensional Free-Vortex Wake (FVW) formulation initially employed in AeroROTOR. This versatile aeroelastic simulation tool is implemented within the framework of MATLAB Simulink/Simscape-Multibody©, a modular environment suitable for industry analysts, researchers, and academic users focusing on wind turbine aero-servo-elastic applications. Furthermore, it serves to lay the groundwork for the development of advanced control laws for multi-megawatt rotors, fostering innovation in the design and optimization of the next-generation wind turbines. The presented analyses focus on predicting the aeroelastic behavior of the bottom-fixed NREL 5MW rotor in uniform axial flow over the operating range, complemented by more detailed investigations at the rated condition undergoing inflow with/without wind misalignment (yaw). The study on key performance parameters is conducted by comparing with the higher-fidelity data from available Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) coupled with CFD.

Enhancing Savonius Rotor Performance With Zigzag Surface Investigated at Drag Force, Pressure, and Flow Visualization Analysis

Savonius, a type of vertical-axis wind turbine, is a small-scale energy conversion device suitable for low wind speeds, such as those characteristic of Indonesian wind speeds, yet has low efficiency. Savonius is a drag-type turbine. Drag force on the surface is affected by roughness or wavyness. The purpose of this study is to analyze the impact of applying wavy (zigzag) variations to the concave surface of Savonius blades on their performance. This was achieved by the use of 3D computational fluid dynamics simulation at TSR 0.6 with a velocity inlet of 5 m/s. The model was semicircular, zigzag on the concave surface on semicircular with t = 0.75, t = 0.25, and t = 1 mm. The result of this study's CD maximum is 1,817 at the zigzag model with t = 1 and CD avrg =1.24. The average drag coefficient increased by 14 percent compared to the conventional semicircular rotor. The maximum Cp value is also found at t = 1 mm, which is 0.315. The power coefficient increased by 29 percent compared to the conventional semicircular rotor. The total pressure on the blade shows the highest model with t = 1 mm at the same angle of attack (α = 30). Zigzag on the concave surface affects blade pressure, which improves the performance of the Savonius rotor.

Low-Order Modeling of Stacked Rotor Performance in Hover

Coaxial, corotating (stacked) rotors have shown improved performance compared to conventional rotors, but the optimum configuration is highly sensitive to the rotor parameters. This paper reports the development of a low-order model, blade interaction prediction (BLIP), to efficiently predict the thrust and power of closely spaced rotor blades and quantify the effects of rotor geometry on total and individual stacked rotor performance. BLIP couples a vortex panel method and blade element momentum theory to combine the effects of bound circulation and rotor inflow. A cascade effect in the two-dimensional vortex panel method was implemented to incorporate the effect of airfoils rotating in a circle. Validation was performed with measurements of a 1.108-m-radius fixed-pitch stacked rotor with variable axial and azimuthal spacing, and excellent correlation was observed. It was found that small azimuthal angles and axial spacings are most effective in varying total thrust. The variation of thrust and power with azimuthal spacing was found to be a result of bound circulation, while the variation with axial spacing is due to rotor inflow interactions.

Performance Improvement of Winged Compound Helicopter Due to Differential Flap Deflections

A lift-offset system for a single-rotor-type compound helicopter is proposed to improve the aerodynamic performance in high-speed flight. The proposed system utilizes the differential flap deflections on the fixed wings to produce a rolling moment, which is counteracted by the single main rotor, causing the rotor to operate in a lift-offset state. The performance of the proposed system is evaluated through numerical simulations. At first, the effect of lift offset with regard to lift-share ratio on the rotor performance is investigated. Then, the impact of lift offset due to the differential flaps on the overall effective lift-to-drag ratio is studied. The results show that the lift offset significantly improves the rotor performance and the overall effective lift-to-drag ratios, especially at larger rotor lift-share ratios. The overall effective lift-to-drag ratio increases by 10% due to the differential flaps compared to the zero-flap deflections. It is concluded that the lift offset due to the differential flaps achieves more efficient cruising flight for a single-rotor-type compound helicopter.

Active power control of wind turbine based on fuzzy pitch control

With the continuous increase in wind power penetration rate, wind turbine generators (referred to as WTGs or wind turbines) need to have the capability of active power control (APC) to respond to grid power commands. To reduce the burden of pitch control on wind turbines, existing studies have adopted a technological approach that uses variable-speed operation of the wind rotor instead of pitch control. Typically, pitch control is only initiated at the speed boundaries to limit variable-speed operation within the speed range. However, due to the influence of factors such as wind speed, rotor speed and control parameters, there is a noticeable saturation phenomenon in pitch control at the speed boundaries, which can affect the variable-speed process of the wind rotor and APC performance within the speed range. Therefore, this paper determines whether blade pitch adjustment needs to be performed in advance when the wind turbine operates within the speed range based on the rotor speed state. This avoids the pitch action at the speed boundaries and the associated pitch saturation problem. The results show that the proposed method in this paper reduces the frequency of the rotor speed reaching the speed boundaries by performing pitch actions within the speed range. This alleviates the influence of pitch saturation on the variable-speed process of the wind rotor, as well as the occurrence of overspeed and electromagnetic power drop, thereby improving the APC performance of the wind turbine.

Enhancement of aerodynamic performance of Savonius wind turbine with airfoil-shaped blade for the urban application

The present study introduces a novel rotor configuration with an airfoil-shaped blade, based on the low-speed high-lift FX74-CL5-140 airfoil, for enhancing the performance of the Savonius wind turbine for a practical application in urban areas. The preferment of the present design over the original one with a semicircular shape is confirmed by the sequence of unsteady two-dimensional (2D) numerical simulation. The results demonstrate a new power coefficient peak (up to 16.5 % better than that of the original rotor) could be gained at the tip speed ratio (TSR) of 1.1. The effective working range is further extended to TSR > 0.7 compared to that at TSR > 1.0 in the literature. Insight into the flow dynamic, including pressure, velocity, streamline, and wake analysis, reveals that the thick blade near the overlap region, benefiting in terms of the turbine’s high performance. The airfoil blade increases the momentum energy around the rotor, changes the pressure on the concave side, and varies the origin of the pressure force, leading to an increase in the moment arm with more torque exhibited on the rotor at high TSR. In addition, the proper orthogonal decomposition (POD) analysis is also performed to better understand the flow phenomena behind the rotor. Overall, the present design is beneficial for urban applications because it can enhance the rotor performance without losing the omnidirectional and compactness features.

BEARINGLESS ROTOR SYSTEM MAIN COMPONENTS DESIGNING

Bearingless rotor system design optimizes mechanical simplicity, eliminates frictional losses typical of conventional bearing systems, and improves the overall efficiency of the rotor system. Based on the findings of the research, it is possible to determine that composite materials can be applied in order to improve the performance of the rotorcraft rotor system.A theoretical analysis of the influence of input parameters on the aerodynamic quality of the main rotor of a rotorcraft was carried out. The strength and aerodynamic quality of the designed parts were calculated using the finite element analysis method. The energy efficiency of the use of composite materials is substantiated, which will ensure better efficiency and competitiveness of the aircraft.

Performance analysis of an idealized Darrieus–Savonius combined vertical axis wind turbine

AbstractTo investigate the effect of force distributions of each turbine component on the power performance of the Darrieus–Savonius combined vertical axis wind turbine (hybrid VAWT), the hybrid VAWT is modeled as idealized turbine under various force distributions. The goal of idealization is to simplify the intricate interactions between the Savonius and Darrieus components. The simulation actuator surfaces with uniform force distributions lead to a cost‐effective way to identify the optimal force distribution of each turbine component. The numerical model was validated against momentum theory. The results demonstrated that the numerical and theoretical results yield similar predictions in the low‐thrust cases but show differences in the high‐thrust cases. The maximum power coefficient of an idealized hybrid VAWT with given thrust coefficient is lower than that of a single actuator. This is a consequence of the nonoptimal loading on the actuator. The results indicate that an idealized hybrid VAWT does not show a significant power increase compared with an optimal single Darrieus rotor. Therefore, the presence of a Savonius rotor inside a Darrieus rotor leads to a lower power output in any circumstance. The hybrid configuration is primarily advantageous for the start‐up performance of the combined rotor, which is not explored in this study.

Rotor Performance Predictions for Urban Air Mobility: Single vs. Coaxial Rigid Rotors

This work details the development and validation of a methodology for high-resolution rotor models used in hybrid Blade Element Momentum Theory Unsteady Reynolds Averaged Navier–Stokes (BEMT-URANS) CFD. The methodology is shown to accurately predict single and coaxial rotor performance in a fraction of the time required by conventional CFD methods. The methodology has three key features: (1) a high-resolution BEMT rotor model enabling large reductions in grid size, (2) a discretized set of momentum sources to interface between the BEMT rotor model and the structured URANS flow solver, and (3) leveraging of the first two features to enable highly parallelized GPU-accelerated multirotor CFD simulations. The hybrid approach retains high-fidelity rotor inflow, wake propagation, and rotor–rotor interactional effects at a several orders of magnitude lower computational cost compared to conventional blade-resolved CFD while retaining high accuracy on steady rotor performance metrics. Rotor performance predictions of thrust and torque for both single and coaxial rotor configurations are compared to test the data that the authors obtained at the NASA Langley 14- by 22-ft. Subsonic Tunnel Facility. Simulations were run with both fully turbulent and free-transition airfoil performance tables to quantify the associated uncertainty. Single rotor thrust and torque were predicted on average within 4%. Coaxial thrust and power were predicted within an average of 5%. A vortex ring state (VRS) shielding phenomenon for coaxial rotor systems is also presented and discussed. The results support that this hybrid BEMT-URANS CFD methodology can be highly parallelized on GPU machines to obtain accurate rotor performance predictions across the full spectrum of possible UAM flight conditions in a fraction of the time required by conventional higher-fidelity methods. This strategy can be used to rapidly create look-up tables with hundreds to thousands of flight conditions using a three-dimensional multirotor CFD for UAM.

Two-stage Taguchi-based optimization on dynamically-vented blade flaps to enhance the rotor performance of a Savonius turbine

Among the vertical-axis turbine groups for small-scale wind and hydrokinetic applications, the Savonius type is considered practical due to its simple construction, easy maintenance, and good self-starting characteristics. Unfortunately, it has a poor efficiency due to the exertion of negative torques during its returning sweeps. Recently, the technique of controlled dynamic venting has been shown to reduce this negative torque on a two-bladed Savonius rotor while preserving its omnidirectional capability. That investigation was extended in this numerical study by refining the controllable flaps of the same rotor to improve its performance using a two-stage optimization procedure. In the first stage, the design parameters of the controllable flaps were optimized using the Taguchi and Analysis of Variance (ANOVA) methods. In this analysis, the flap length was found to be the most significant parameter affecting the rotor performance with a contribution ratio of 79.8%, in contrast to a ratio of only 6.7% by the least effective parameter: the flap opening angle. The first optimization stage produced an improvement of 16.7% on the average power coefficient (CP) of the vented rotor, compared to the unvented one, at the optimal tip-speed ratio (TSR) of 1.0. In the second stage, the flap length was refined further to a shorter flap of 22.5% of the blade length, resulting in an improvement of 21% on the same metric at the same TSR. Crucially, these controllable flaps only used an energy cost of 6.1% of the total energy produced by the rotor, a significant improvement from the 12.2% energy cost obtained in the previous study.