Design Of Wind Turbine Rotors Research Articles

Effect of the Phase-Shift Angle on the vertical axis Savonius wind turbine performance as a renewable-energy harvesting instrument

Wind energy is the third-largest renewable energy source after hydro and solar energy, so it has great potential in increasing renewable energy as a percentage of national energy. However, wind energy installation is only at 0.25% of the existing potential; so, it still needs to be developed. One of the development efforts is to optimize the wind turbine rotor design. Savonius rotors are among the most popular rotors to convert wind energy into electrical energy. The Savonius turbine is a simple structure, easy to modify to upgrade Savonius performance, and can be operated at low velocity. Phase-shift angles of 0°, 30°, 60°, and 90° were utilized in this study on a two-stage Savonius wind turbine. This study was carried out using Solver CFX utilizing the Computational Fluid Dynamic technique on the ANSYS Student version software. An SST (shear stress transport) turbulence model with steady-state turbulence was used. The purpose of this study was to assess the influence of PSA on the performance of the Savonius two-stage turbine. Factorial design analysis was used in conjunction with the CFD approach. The results indicated that PSA influenced the Savonius turbine’s performance, with 30° being the optimal PSA. Simultaneously, the Cpmax may be obtained using 0.29. The factorial design study with two components revealed that the Phase-Shift Angle had a considerable effect on rotor performance, and the two factors (TSR and PSA) had an interaction.

Using Small Wind Turbine Technology to Design an AntiFrost Fan

Anti-frost fans (AFFs) are widely used in agriculture to reduce the frost damage to crops. The small wind turbine rotor design code (SWRDC) was adapted to design the blades of an anti-frost fan to maximize the mass flow rate through the rotor while minimizing the blade mass and aerodynamic noise. Using a random sample set of 60 baseline designs, the design is iterated using a genetic algorithm to obtain an optimized design with a mass flow rate of 3.11 kg/s, a blade mass of 6.96 kg, and with a noise level of 72.8 dB.

Towards the development of an advanced wind turbine rotor design tool integrating full CFD and FEM

Large, highly flexible wind turbines of the new generation will make designers face un-precedent challenges, mainly connected to their huge dimensions. To tackle these challenges, it is commonly acknowledged that design tools must evolve in the direction of both improving their accuracy and turning into holistic, multiphysics tools. Furthermore, the wind turbine industry is reaching a high level of maturity, and ever more accurate and reliable design tools are required to further optimise these machines. Within this framework, the study shows the development of an integrated platform for blade design integrating 3D CFD flow simulations and 3D-FEM structural analysis. Artificial intelligence techniques are applied to develop an optimization procedure based on the proposed tool. The potential of the new platform has been tested on the well-known test case of the MEXICO rotor, for which an optimization of the blade design has been carried out. Exploring a design space sampled with 2000 CFD and FEM computations, increases in blade torque have been obtained at each of the three tip-speed ratios (TSR) investigated, ranging from 6% at the nominal TSR to 14% at the lowest one, while stresses on the blade are kept almost unaltered.

Editorial: Towards Innovation in Next Generation of Wind Turbine Rotor Design

Editorial: Towards Innovation in Next Generation of Wind Turbine Rotor Design

Full scale rotor blade deformation measurements in comparison with aeroelastic simulations based on measured high-resolution wind fields

Aeroelasticity is one of the biggest challenges in wind turbine rotor design, as the length of rotor blades increases which comes along with a slenderer design. The knowledge of the aeroelastic turbine behavior is of great importance. A comparison to field measurements is of huge importance when validating aeroelastic tools. However, the measurement of deformation and torsion in the field is not trivial and the conduction of realistic post-test simulations is a challenge. One crucial factor for these simulations is the wind field, which needs to be captured in a high spatial and temporal resolution. In this paper, the results of deformation measurements conducted in the field with an optical measurement method called Digital Image Correlation (DIC) on one rotor blade will be shown and compared to aeroelastic post-test simulations using highly resolved wind fields measured with a SpinnerLidar.

Wind turbine rotor design under wind farm control laws

In this work, we investigate the impact of different wind farm control techniques on the structural design of a 10MW reference wind turbine. Active wake mixing and wake redirection have been recently proposed as a way to reduce wake-turbine interference in a wind farm and both show potential for improving the overall power production. However, such controllers modify the dynamic behaviour of the individual turbine, so that a thorough assessment of the resulting loads and displacements becomes necessary. In fact, as most wind turbines are designed according to international standards, one or more structural constraints are active on the final design, meaning that an increase of the sizing loads, or deflections, would make necessary to modify the structural layout. To investigate these aspects, we compare three redesigns of the same rotor: the first is equipped with a standard controller, while the second and the third integrate different wind farm controllers. All the solutions are optimized with our in-house design tool so that the three configurations emerge from the same design process. Results are then compared in terms of ultimate and fatigue loads, displacements and blade mass.

An efficient approach to explore the solution space of a wind turbine rotor design process

This study proposes a novel approach to explore the solution space of a wind turbine rotor design process. The goal is to offer to blade designers the possibility to select an optimal rotor for given market conditions, assessing trade-offs and alternatives in a matter of minutes. The design process consists of sequential aerodynamic-structural optimizations, where the two loops are linked via a blade-loading parameter that can be varied by the user. A design study is performed starting from the IEA Wind Task 37 land-based reference wind turbine. The solution space is characterized for rotor diameters in the range of 130–160 m, rated generator power values in the range of 3.0–6.0 MW, and tip-speed ratios in the range of 7.5–12.5. Results are discussed highlighting optimal design decisions and trade-offs.

Improvement of aerodynamic performance of a small wind turbine

The aerodynamic performance of horizontal-axis wind turbines is strongly dependent on many parameters, among which the airfoil type and the blade geometry (mainly defined by the chord and the twist distributions) are considered the most critical ones. In this article, an approach giving the appropriate airfoil for a small wind turbine design was conducted by performing an aerodynamic improvement of the blade’s airfoil. First, a preliminary design of the rotor blades of a small wind turbine (11 kW) was conducted using the small wind turbine rotor design code. This preliminary approach was done for different airfoils, and it resulted in a maximum power coefficient of 0.40. Then, the aerodynamic efficiency of the wind turbine was improved by modifying the geometry of the airfoils. This technique targets the optimization of the lift-to-drag ratio (Cl/Cd) of the airfoil within a range of angles of attack. Also, a non-uniform rational B-spline approximation of the airfoil was adopted in order to reduce the number of the design variables of the optimization. This methodology determined the best airfoil for the design of a small wind turbine, and it gave an improved power coefficient of 0.42.

Gravo-aeroelastic scaling of very large wind turbines to wind tunnel size

This work focuses on the design of wind turbine rotors of wind tunnel size that match the aerodynamic (for both rotor and wake) and aeroelastic behavior of multi-MW machines, including gravitational effects. The approach follows the classical definition of length, time and mass scaling ratios to respect nondimensional scaling parameters. The sub-scale model is obtained by a complete aero-structural re-design procedure, considering airfoils with similar polars at sub-scale Reynolds and the use of adequate materials. The approach is applied to the design of a sub-scale wind tunnel rotor that mimics the behavior of a 10 MW wind turbine. Results illustrate the main characteristics of the proposed method as well as its limitations, highlighting the challenges posed by representing a gravo-aeroelastic system at a much reduced scale.

Comparison of classical methods for blade design and the influence of tip correction on rotor performance

The classical blade-element/momentum (BE/M) method, which is used together with different types of corrections (e.g. the Prandtl or Glauert tip correction), is today the most basic tool in the design of wind turbine rotors. However, there are other classical techniques based on a combination of the blade-element approach and lifting-line (BE/LL) methods, which are less used by the wind turbine community. The BE/LL method involves different interpretations for rotors with finite or infinite numbers of blades and different assumptions with respect to the optimum circulation distribution. In the present study we compare the performance and the resulting design of the BE/M method by Glauert [1] and the BE/LL method by Betz [2] for finite as well as for infinite-bladed rotors, corrected for finiteness through the tip correction.In the first part of the paper, expressions are given for the optimum design, including blade plan forms and local pitch distributions. The comparison shows that the resulting geometry of the rotor depends on the method used, but that the differences mainly exist in the inner part of the blade and at relatively small tip speed ratios (TSR<5). An important conclusion is that an infinite-bladed approach combined with a tip correction results in a geometry which is nearly identical to a geometry generated from a finite-bladed approach.Next, the results from an experimental investigation on the influence on rotor performances of the tip correction on two different rotors are presented. Employing BE/M without the tip correction (“Glauert rotor”) and BE/LL with the Goldstein's circulation (“Betz rotor”) two different 3-bladed rotors were designed and manufactured. The two rotors were investigated experimentally in a water flume to compare their performance at different tip speed ratios and pitch angles. As a result of the comparison it was found that the Betz rotor had the best performance.

Large Wind Turbine Rotor Design using an Aero-Elastic / Free-Wake Panel Coupling Code

Despite the advances in computing resources in the recent years, the majority of large wind-turbine rotor design problems still rely on aero-elastic codes that use blade element momentum (BEM) approaches to model the rotor aerodynamics. The present work describes an approach to wind-turbine rotor design by incorporating a higher-fidelity free-wake panel aero-elastic coupling code called MIRAS-FLEX. The optimization procedure includes a series of design load cases and a simple structural design code. Due to the heavy MIRAS-FLEX computations, a surrogate-modeling approach is applied to mitigate the overall computational cost of the optimization. Improvements in cost of energy, annual energy production, maximum flap-wise root bending moment, and blade mass were obtained for the NREL 5MW baseline wind turbine.

Aerodynamic wind-turbine rotor design using surrogate modeling and three-dimensional viscous–inviscid interaction technique

In this paper a surrogate optimization methodology using a three-dimensional viscous-inviscid interaction code for the aerodynamic design of wind-turbine rotors is presented. The framework presents a unique approach because it does not require the commonly-used blade element momentum (BEM) method. The three-dimensional viscous-inviscid interaction code used here is the accurate and fast MIRAS code developed at the Technical University of Denmark. In comparison with BEM, MIRAS is a higher-fidelity aerodynamic tool and thus more computationally expensive as well. Designing a rotor using MIRAS instead of an inexpensive BEM code represents a challenge, which is resolved by using the proposed surrogate-based approach. As a verification case, the methodology is applied to design a model wind-turbine rotor and is compared in detail with the one designed with BEM. Results demonstrate that nearly identical aerodynamic performance can be achieved using the new design method and that the methodology is effective for the aerodynamic design of wind-turbine rotors.

Straight-bladed vertical axis wind turbine rotor design guide based on aerodynamic performance and loading analysis

Vertical axis wind turbines with straight blades are attractive for their relatively simple structure and aerodynamic performance. An efficient design methodology is required to enhance this resurging renewable energy technology. This paper aims to provide a robust design procedure built on an existing analytical approach to determine the optimum range of the design parameters for prototype construction. Identifying the proper range of design parameters can save significant time and resources in the initial turbine development stages. Here the double-multiple streamtube method has been utilized to analyze turbine aerodynamic performance. A parametric optimization has been performed for several design factors to maximize the turbine power coefficient and its operational range. The results show that the optimum value of the rotor solidity factor, blade aspect ratio, and rotor aspect ratio are in the range of 0.2 &lt; σ &lt; 0.6, 10 &lt; μ &lt; 20, and 0.5 &lt; H/ D &lt; 2, respectively. Aerodynamic loading analysis has also been carried out, and the most severe stresses acting on the blades and supporting arms were determined. The most favorable bending stress distribution along the blade occurred when two supporting arms per blade were used at intermediate locations of 21% and 79% along the blade length. A comparative study of different supporting arm shapes demonstrated that utilizing aerodynamic profiles for turbine arms created the most acceptable aerodynamic response. A summary of design aspects addressed in this paper is presented in a useful summary flowchart.

Optimization of Aerodynamic Performance of Wind Turbine Blades

A wind-power generation system uses wind turbine blades to convert the kinetic energy of wind to drive a generator which in turn yields electricity, the aerodynamic performance of the wind turbine blades has decisive effect on the cost benefit of the whole system. The aerodynamic analysis and the optimization of design parameters for the wind turbine blades are key techniques in the early stage of the development of a wind-power generation system. It influences the size selection of connecting mechanisms and the specification of parts in the design steps that follows. A computational procedure and method for aerodynamics optimization was established in this study for three-dimensional blades and the rotor design of a wind turbine. The procedure was applied to improving a previously studied 25kW wind turbine rotor design. Results show that the aerodynamic performance of the new three-dimensional blades has remarkable improvement after optimization.

Inverse design-momentum, a method for the preliminary design of horizontal axis wind turbines

Wind turbine rotor prediction methods based on generalized momentum theory BEM routinely used in industry and vortex wake methods demand the use of airfoil tabulated data and geometrical specifications such as the blade spanwise chord distribution. They belong to the category of "direct design" methods. When, on the other hand, the geometry is deduced from some design objective, we refer to "inverse design" methods. This paper presents a method for the preliminary design of wind turbine rotors based on an inverse design approach. For this purpose, a generalized theory was developed without using classical tools such as BEM. Instead, it uses a simplified meridional flow analysis of axial turbomachines and is based on the assumption that knowing the vortex distribution and appropriate boundary conditions is tantamount to knowing the velocity distribution. The simple conservation properties of the vortex components consistently cope with the forces and specific work exchange expressions through the rotor. The method allows for rotor arbitrarily radial load distribution and includes the wake rotation and expansion. Radial pressure gradient is considered in the wake.The capability of the model is demonstrated first by a comparison with the classical actuator disk theory in investigating the consistency of the flow field, then the model is used to predict the blade planform of a commercial wind turbine. Based on these validations, the authors postulate the use of a different vortex distribution (i.e. not-uniform loading) for blade design and discuss the effect of such choices on blade chord and twist, force distribution and power coefficient. In addition to the method's straightforward application to the pre-design phase, the model clearly shows the link between blade geometry and performance allowing quick preliminary evaluation of non uniform loading on blade structural characteristics.

Sensitivity of Key Parameters in Aerodynamic Wind Turbine Rotor Design on Power and Energy Performance

In this paper the influence of different key parameters in aerodynamic wind turbine rotor design on the power efficiency, Cp, and energy production has been investigated. The work was divided into an analysis of 2D airfoils/blade sections and of entire rotors. In the analysis of the 2D airfoils it was seen that there was a maximum of the local Cp for airfoils with finite maximum Cl/Cd values. The local speed ratio should be between 2.4 and 3.8 for airfoils with maximum cl/cd between 50 and 200, respectively, to obtain maximum local Cp. Also, the investigation showed that Re had a significant impact on CP and especially for Re<2mio corresponding to rotors below approximately 400kW this impact was pronounced. The investigation of Cp for rotors was made with three blades and showed that with the assumption of constant maximum cl/cd along the entire blade, the design tip speed ratio changed from X=6 to X=12 for cl/cd=50 and cl/cd=200, respectively, with corresponding values of maximum cp of 0.46 and 0.525. An analysis of existing rotors re-designed with new airfoils but maintaining the absolute thickness distribution to maintain the stiffness showed that big rotors are more aerodynamic efficient than small rotors caused by higher Re. It also showed that the design tip speed ratio was very dependent on the rotor size and on the assumptions of the airfoil flow being fully turbulent (contaminated airfoil) or free transitional (clean airfoil). The investigations showed that rotors with diameter D=1.75m, should be designed for X around 5.5, whereas rotors with diameter D=126m, should be designed for Xbetween 6.5 and 8.5, depending on the airfoil performance.