Enhancement of wind turbine aerodynamic performance by a numerical optimization technique (original) (raw)

Wind Turbine Blade Aerodynamic Design and Optimization

American International Journal of Contemporary Research

Traditionally, the aerodynamic design of a wind turbine blade depends on the choice of one or more airfoils to be used along its span. The experience and ability of the designer is necessary at this phase of the design processes. The method developed in this paper intends to mitigate this need. A genetic algorithm is specially designed to determinate the aerodynamic design parameters of the blades and the selection of the airfoils. This first approach uses thin airfoil theory. The Blade Element Momentum Method is used as fitness function for the evaluation of each individual's power coefficient within the domain considered by the genetic algorithm. The study case of this paper achieved good results, reaching power coefficients greater than 55%, figure close to the theoretical limit of 59% defined by the conservation of linear momentum theory.

Computational aerodynamic optimisation of vertical axis wind turbine blades

The approach and results of a parametric aerodynamic optimisation study is presented to develop the blade design for a novel implementation of a vertical axis wind turbine. It was applied to optimise the two-dimensional cross-sectional geometry of the blades comprising the turbine. Unsteady viscous computational fluid dynamic simulations were used to evaluate blade performance. To compare geometries, the non-dimensional coefficient of power was used as a fitness function. Moving meshes were used to study the transient nature of the physical process. A new parameterisation approach using circular arcs has been developed for the blade cross sections. The optimisation process was conducted in two stages: firstly a design of experiments based response surface fitting was used to explore the parametric design space followed by the use of a Nelder–Mead simplex gradient-based optimisation procedure. The outcome of the optimisation study is a new blade design that is currently being tested in full-scale concept trials by a partnering wind energy company.

New Approach to High-Fidelity Aerodynamic Design Optimization of a Wind Turbine Blade

International Journal of Renewable Energy Research, 2013

A new approach to high-fidelity aerodynamic design optimization of a wind turbine blade configuration is offered. This method combines Blade Element Momentum (BEM) theory with the high fidelity aerodynamic shape optimization of an airfoil. The chord length and the twist angle of the blade at various radiuses have been calculated by BEM. The Navier Stokes equations are solved to simulate both two and three dimensional flows. The Results which are obtained from 2D Computational Fluid Dynamics (CFD) have been utilized to train a Neural Network (NN). E387Eppler is used as the base cross section of the blade. In the process of airfoil optimization, Genetic Algorithm (GA) is coupled with trained NN to attain the best airfoil shape at each angle of the attack. The simulation and validation of the base wind turbine with calculated pitch angle, twist angle, chord profile and base airfoil have been performed. The comparison of the results of this turbine with optimized one, illustrates a sign...

Wind Turbine Blade Design with Computational Fluid Dynamics Analysis

2017

Although there are many blade profile have been improved for use in aviation and energy sector, there is still needed blade profiles which have higher performance especially the commercial horizontal axis wind turbine efficiency is taken into account. The purpose of this study is to obtain the new blade profiles which have higher lift (CL) and drag (CD) coefficients for wind turbine making geometric modifications on several NACA wing profile systematically. For this purpose, the performance of NACA and developed new profiles have been compared with each other using computational fluid dynamics analysis and it is seen that the new developed profiles have higher performance than NACA profiles. Later on, according to the Blade Element Momentum Theory (BEM Theory) turbine blades are designed with developed new profiles and 3-dimensional CFD analyses are performed. Increase in torque in the wind turbine is determined.

Aerodynamic Optimization of Airfoil Profiles for Small Horizontal Axis Wind Turbines

Computation

The purpose of this study is the development of an automated two-dimensional airfoil shape optimization procedure for small horizontal axis wind turbines (HAWT), with an emphasis on high thrust and aerodynamically stable performance. The procedure combines the Computational Fluid Dynamics (CFD) analysis with the Response Surface Methodology (RSM), the Biobjective Mesh Adaptive Direct Search (BiMADS) optimization algorithm and an automatic geometry and mesh generation tool. In CFD analysis, a Reynolds Averaged Numerical Simulation (RANS) is applied in combination with a two-equation turbulence model. For describing the system behaviour under alternating wind conditions, a number of CFD 2D-RANS-Simulations with varying Reynolds numbers and wind angles are performed. The number of cases is reduced by the use of RSM. In the analysis, an emphasis is placed upon the role of the blade-to-blade interaction. The average and the standard deviation of the thrust are optimized by a derivative-free optimization algorithm to define a Pareto optimal set, using the BiMADS algorithm. The results show that improvements in the performance can be achieved by modifications of the blade shape and the present procedure can be used as an effective tool for blade shape optimization. a GA for the optimization of the aerodynamic performance of horizontal axis wind turbine blades. Clifton-Smith and Wood [8] applied differential evolution strategies to optimize numerically small wind turbine blades with the double purpose of maximizing power coefficient and minimizing starting time. Here, the power coefficient was calculated by the standard BEM theory.

Shape Optimization of Wind Turbine Blades

This paper presents a design tool for optimizing wind turbine blades. The design model is based on an aerodynamic/aero-elastic code that includes the structural dynamics of the blades and the Blade Element Momentum (BEM) theory. To model the main aero-elastic behaviour of a real wind turbine, the code employs 11 basic degrees of freedom corresponding to 11 elastic structural equations. In the BEM theory, a refined tip loss correction model is used. The objective of the optimization model is to minimize the cost of energy which is calculated from the annual energy production and the cost of the rotor. The design variables used in the current study are the blade shape parameters, including chord, twist and relative thickness. To validate the implementation of the aerodynamic/aero-elastic model, the computed aerodynamic results are compared to experimental data for the experimental rotor used in the European Commision-sponsored project Model Experiments in Controlled Conditions, (MEXICO) and the computed aero-elastic results are examined against the FLEX code for flow past the Tjaereborg 2 MW rotor. To illustrate the optimization technique, three wind turbine rotors of different sizes (the MEXICO 25 kW experimental rotor, the Tjaereborg 2 MW rotor and the NREL 5 MW virtual rotor) are applied. The results show that the optimization model can reduce the cost of energy of the original rotors, especially for the investigated 2 MW and 5 MW rotors.

High-fidelity aerodynamic shape optimization of wind turbine blades

Recent improvements in accuracy and efficiency of numerical simulation techniques in the field of engineering have led to an increasing interest in applying high-fidelity models for wind turbine design. Computational Fluid Dynamics (CFD) based on Reynolds-Averaged Navier-Stokes (RANS) equations in a co-rotating reference frame has shown promising results for performing design analysis. However, using high-fidelity techniques for wind turbine blade design optimization is not yet fully understood. Especially, high-fidelity aerodynamic shape optimization for wind turbine blades has not yet been employed in the industry due to its computational inefficiency when large number of design variables are used with traditional techniques such as finite difference derivatives and gradient-free optimization methods. This dissertation presents an efficient and robust high-fidelity aerodynamic shape optimization methodology for rotating flow problems. The high-fidelity optimization method consists of a multi-block, structured RANS-based CFD simulation tool, a discrete adjoint method, a shape parametrization method, a mesh perturbation technique and a gradient-based optimizer. Steady-state solutions are obtained by the RANS-based CFD analysis method based on a co-rotating reference frame. The turbulence model is a segregated one-equation SA model. Total derivatives of the flow solution and constraint(s) are computed by a discrete adjoint method. For reducing the computational cost of computing partial derivatives that are required in the discrete adjoint method, forward automatic differentiation is used. Once the total derivatives and flow solution are computed, the gradient-based optimizer based on sequential quadratic programming computes a better design by using an augmented Lagrangian formulation with quasi-Newton approximations for the Hessian. The change in design variables obtained by the optimizer is parametrized with a Free Form Deformation (FFD) volume approach. After performing surface perturbations, the mesh is deformed using a hybrid mesh deformation scheme, that combines an algebraic and linear elasticity method. The linear elasticity method based on finite elements is used for large perturbations, while the algebraic method attenuates small perturbations. When the optimality condition is satisfied, the iterative procedure ends with the optimal design. Verification and validation of the developed codes are performed using the NREL VI wind turbine. The RANS-based CFD solver is validated by comparing numerical results with NREL VI sequence S experimental data. The solver resolves attached flow conditions accurately, while separated flow conditions lead to inaccurate flow solutions due to insufficient transition and turbulence modelling. DES can resolve the inaccuracy associated with separated flow conditions. Total derivatives of the adjoint method are verified by comparing derivatives of the complex and finite difference method. The quality of (perturbed) meshes are verified by using mesh quality metrics. Correct shape parametrization is assured after careful examining the direction and magnitude of the deformations. Since the NREL VI wind turbine blade rotates at a constant angular velocity, the power generation is considered to be only dependent on torque. Therefore, the objective of the optimization is maximizing the torque coefficient with shape, twist, and pitch design variables. Thickness constraints between 15% and 50% are added for representing a wing box. The thickness constraints impose thicknesses of the blade to increase only up to 300% of the original thickness. No reduction in thickness with respect to the baseline design at that region of the blade is possible in order to fit the original wing box. For future research, the objective and constraint function(s) can be easily adapted to more realistic and modern rotating flow problems. From the aerodynamic shape optimization of the NREL VI blade, an increase of at least 22.4% in torque is achieved. The airfoil shapes tends to become more cambered and less thick. The nose of the airfoil is more aligned to the inflow. At root section of the wind turbine blade, the trailing edge of the airfoil acts as a flap in order to obtain higher loads at low relative velocity. Three different mesh refinements are employed for optimization. The first mesh is a coarse mesh that is used for verification purposes of the optimization procedure. The second mesh is employed for obtaining accurate aerodynamic shape optimization results. The final design variable values of the medium refined mesh are projected on the most refined mesh, because computational costs would be too high for performing optimization. An increase of 29.1% in torque is achieved, indicating that the increase in optimized torque for more refined meshes will be higher when using coarser meshes. Since wind turbines are operating in a range of wind speeds, multipoint optimization from cut-in to rated wind speed is performed. Similar results as in single-point optimization are achieved. An increase of 22.2% in Annual Energy Production AEP is obtained. The adjoint method and high-fidelity aerodynamic shape optimization methodology allow designers to examine accurately the trade-off between various design variables at the early stage of the design process. For future research purposes, aerostructural and aeroelasticity optimization can be employed with the same framework.

Airfoil Boundary Layer Optimization Toward Aerodynamic Efficiency of Wind Turbines

Flight Physics - Models, Techniques and Technologies, 2018

This chapter describes the method of airfoil optimization considering boundary layer for aerodynamic efficiency increment. The advantages of laminar boundary layer expansion in airfoil of horizontal axis wind turbine (HAWT) blades are presented as well. The genetic algorithm (GA) optimization interfaced with the flow solver XFOIL was used with multiobjective function. The power performance of turbine with optimized airfoil was calculated by using blade element method (BEM) in software QBlade. The CFD simulation from OpenFOAM ® with Spalart-Allmaras turbulence model showed the visualized airflow. The optimized airfoil shows enlarged laminar boundary layer region in all flow regime with a higher aerodynamic efficiency and the increased gliding ratio (GR). The power velocity and annual energy production (AEP) curves show the performance improvement of wind turbine with the optimized airfoil. The boundary layer thickness and skin-friction coefficient values support the decreased drag of the optimized airfoil. The smaller laminar separation bubbles and reduced stall regime of CFD simulations illustrate the desirable aerodynamics of the resulted airfoil.

Torque-Matched Aerodynamic Shape Optimization of HAWT Rotor

Journal of Physics: Conference Series, 2014

Schmitz and Blade Element Momentum (BEM) theories are integrated to a gradient based optimization algorithm to optimize the blade shape of a horizontal axis wind turbine (HAWT). The Schmitz theory is used to generate an initial blade design. BEM theory is used to calculate the forces, torque and power extracted by the turbine. The airfoil shape (NREL S809) is kept the same, so that the shape optimization comprises only the chord and the pitch angle distribution. The gradient based optimization of the blade shape is constrained to the torque-rotational speed characteristic of the generator, which is going to be a part of the experimental set-up used to validate the results of the optimization study. Hence, the objective of the optimization is the maximization of the turbines power coefficient Cp while keeping the torque matched to that of the generator. The wind velocities and the rotational speeds are limited to those achievable in the wind tunnel and by the generator, respectively. After finding the optimum blade shape with the maximum Cp within the given range of parameters, the Cp of the turbine is evaluated at wind-speeds deviating from the optimum operating condition. For this purpose, a second optimization algorithm is used to find out the correct rotational speed for a given wind-speed, which is again constrained to the generator's torque rotational speed characteristic. The design and optimization procedures are later validated by high-fidelity numerical simulations. The agreement between the design and the numerical simulations is very satisfactory.

Multi-Objective Aerodynamic and Structural Optimization of Horizontal-Axis Wind Turbine Blades

A procedure based on MATLAB combined with ANSYS is presented and utilized for the multi-objective aerodynamic and structural optimization of horizontal-axis wind turbine (HAWT) blades. In order to minimize the cost of energy (COE) and improve the overall performance of the blades, materials of carbon fiber reinforced plastic (CFRP) combined with glass fiber reinforced plastic (GFRP) are applied. The maximum annual energy production (AEP), the minimum blade mass and the minimum blade cost are taken as three objectives. Main aerodynamic and structural characteristics of the blades are employed as design variables. Various design requirements including strain, deflection, vibration and buckling limits are taken into account as constraints. To evaluate the aerodynamic performances and the structural behaviors, the blade element momentum (BEM) theory and the finite element method (FEM) are applied in the procedure. Moreover, the non-dominated sorting genetic algorithm (NSGA) II, which constitutes the core of the procedure, is adapted for the multi-objective optimization of the blades. To prove the efficiency and reliability of the procedure, a commercial 1.5 MW HAWT blade is used as a case study, and a set of trade-off solutions is obtained. Compared with the original scheme, the optimization results show great improvements for the overall performance of the blade.