New morphing blade section designs and structural solutions for smart blades

Within INNWIND.EU new concepts are investigated having the ultimate goal to reduce the cost per kilowatt-hour of the produced energy. With increasing size of wind turbines, new approaches to load control are required to reduce the stresses in blades. Experimental and numerical studies in the fields of helicopter and wind turbine blade research have shown the potential of shape morphing in reducing blade loads.

Morphing technologies, along with other control concepts, are investigated under Task 2.3 of WP “Lightweight Rotor”, against aerodynamic compliance and requirements of the complete wind turbine system. As these efforts mature from an aeroelastic and control point of view, in order to get to the next stage of applying the solutions on wind turbine systems evaluation of the structural needs of the various proposed solutions and quantification of their potential is required.

The report includes the efforts performed within Task 2.2 “Lightweight structural design” of INNWIND.Eu work-package WP2 “Lightweight Rotor” regarding the structural solutions necessary to accommodate the requirements of smart blades developed within work-package WP2 Task 2.3 “Active and passive loads control and alleviation (smart blades) design”.

The research performed within Task 2.2 and reported herein does not cover investigations for the complete set of design requirements of smart blades, such as aerodynamic control surface size. Rather it focuses on answers relevant to integration within the blade structure, i.e. no loss of local/global stiffness or strength and/or fatigue life.

The purpose is to report efforts towards the use of new morphing blade section designs and the structural solutions for smart blades (developed in Task 2.3). The objective is to define, assess and demonstrate innovative concepts for lightweight rotor blades through the synergistic combination of adaptive characteristics from passive built-in geometrical couplings and active control.

The investigations performed on the blade sections with variable geometry airfoils were designed and assessed towards compliance with structural constraints and manufacturing processes constraints. Down selection of design based on results of analysis (for input to Task 2.3) was also performed. Following solutions were investigated:  Morphing blade sections with Shape Memory Alloys (SMA) by University of Patras  Morphing blade sections using an elastomer of zero Poisson ratio by University of Bristol  Morphing blade sections involving an innovative mechanism by Denmarks University of Technology The work performed on these three concepts is described in individual chapters of the present report.

Section 2 discusses the concept using shape memory alloys, section 3 the concept using the special properties elastomer and section 4 the structural investigations on the blade that should support the innovative mechanism. The advantages and disadvantages of these concepts are discussed in the individual sections, while an overall assessment is performed in the last section of the present report.

The solutions using Shape Memory Alloys, as well as an elastomer of zero Poisson ratio have a quite low technological readiness level (TRL). Both are inspired through the aeronautics sector, yet there are different challenges to address when designing for wind turbine blades. The size in addition with the loading on the component combined with low (or even no) maintenance during the 20-30 years of the blade service life makes fatigue of special importance for these solutions.

Relevant to the morphing blade comprising an innovative mechanism, the focus lays into the elastic stability (buckling) of the supporting structure, i.e. the blade, which needs to be modified to accommodate the mechanism. INNWIND.EU, Deliverable 2.23, New morphing blade section designs & structural solutions for smart blades The technology readiness level (TRL) of the three solutions ranges from 4-6 for wind turbine system applications.

Feasibility studies have been undertaken by looking at the complete system by numerical applications and at details of the concepts through dedicated experiments. Through the efforts performed and presented in this report an advance of this level has been achieved. For all cases the investigations have been conducted with reference to the DTU 10MW reference wind turbine used as the baseline for research activities performed within INNWIND.EU.

Due to the initial stages of the concept development, several configurations and several sensitivity studies have been performed to support the results. These are all described within the present report.