Session: 05-06-01: Lightweight Sandwich Composites and Layered Structures

Paper Number: 113348

113348 - Efficient Modeling of Blades via Beam Element in the Multi-Objective Optimization of Small Wind Turbine Blades 

The performance and safety of wind turbines depend critically on the blade shape. Since blades play a pivotal role in capturing wind energy, design and optimization of wind turbine blades have received a detailed coverage in the literature. Generally, the blade design consists of a multi-objective optimization procedure where maximizing the power output and reducing the blade cost are usually the ultimate goals. More specific to the small wind turbine blade (SWT), the minimization of the starting time of the turbine is also a design objective that should be included in the optimization since small wind turbines have no pitch adjustment and they operate at very low Reynolds number with poor lift to drag property when starting. Multi-objective optimization of SWT blades requires a reliable and efficient structural analysis method. Structural metrics involved in the optimization of the wind turbine blade, either through the constraints or in the objective function itself in a multi-objective optimization framework, must be calculated utilizing computationally efficient structural analysis methods.

In this paper, a study is conducted to ascertain an efficient structural analysis method to be included in the multi-objective optimization of small wind turbine (SWT) blades. For this purpose, initially aerodynamic optimization of a SWT blade is performed utilizing a multi-objective function including the power output and the starting time. Structural analyses of the aerodynamically optimized blade are performed utilizing different fidelity finite element models for justifying the use of the reduced-order finite element (FE) model with beam elements. As a reference, higher fidelity three-dimensional (3-D) FE analyses of the blade are performed and alternative 1-D beam-blade models are evaluated utilizing the results of 3-D FE solutions. In this respect, tapered and multi-section non-tapered 1-D beam-blade model alternatives are evaluated as potential lower fidelity reduced-order models to be employed as efficient structural solvers in a future multi-objective optimization of the small wind turbine (SWT) blade. It is noted that during the aerodynamic optimization of the blade, especially in cases when meta-heuristic optimization methods are employed, blade geometries with unsmooth section transitions can be encountered since meta-heuristic optimization is based on a random search such that spanwise chord and twist distributions are generated randomly for each blade element in each iteration. Tapered and multi-section non-tapered beam-blade models are initially evaluated in terms of their robustness in handling unsmooth section transitions and then in terms of their accuracy by comparing their structural responses with the higher fidelity 3-D FE solutions of the blade at the rated power condition. It is shown that the multi-section non-tapered beam-blade FE model of the SWT blade is a robust model which handles unsmooth section transitions effectively unlike the tapered beam-blade model and it can be used effectively in a future constrained optimization involving the structural metrics as constraints and/or objective functions. On the other hand, discretization problems may arise when tapered beams are used to model the blade when blade section transitions are not smooth; hence no solution can be obtained.

Within the scope of the present study, an automatic beam-blade generator and analyzer is also developed. The automatic beam-blade generator utilizes multi-section non-tapered beam elements and it can be integrated into an aerodynamic optimizer seamlessly without interference. With the developed automatic beam-blade generator and analyzer, commonly used airfoils in SWT blades are evaluated in terms of maximum stress and deflection generated in the rated-power load conditions of a selected baseline blade. Moreover, we also show that the developed automatic beam-blade generator and analyzer can be used to build reliable surrogate models for very fast evaluation of structural metrics in the course of iterations during a SWT blade optimization.

Presenting Author: Altan Kayran Middle East Technical University

Presenting Author Biography: Altan Kayran is a full time professor in the department of Aerospace Engineering in Middle East Technical University in Ankara, Turkey. His research interests are wind turbine aeroelasticity and loads, multi-disciplinary optimization of aerospace structures, mechanics of composite materials, variable stiffness composites.

Authors:

Altan Kayran Middle East Technical University
Demirkan Çöker Middle East Technical University
Can Muyan Middle East Technical University
Onur Ali Batmaz Middle East Technical University
Abolfazl Pourrajabian Department of Energy, Materials and Energy Research Center
David Wood University of Calgary