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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Advanced rotor technologies' taking place on Tuesday, 11 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Hervé LE SOURNE Nantes University - ICAM, France
Co-authors:
Hervé LE SOURNE (1) F P Gilles PAYEN (3) Maeva SABRE (2)
(1) Nantes University - ICAM, Carquefou, France (2) CSTB, Nantes, France (3) fondation océan vital, les sables d'olonnes, France

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Abstract

Structural optimization of vertical axis wind turbine using wind tunel tests and non linear simulation

Introduction

Recent years have seen more focus on the development of small sized wind turbines aimed to urban or remote
areas. For this reason, vertical axis wind turbines present an attractive alternative to horizontal axis wind
turbines in the environment of fluctuating wind.In Nantes Region, the intention is to develop small generators
that can be used as power supply for remote residences, ships, or any residence in urban areas in order to
reduce the consumption from the general power grid. This served the basis for the development of a series of
VAWTs in the framework of the Aerojoules Project.


Approach

This work is oriented to the study and development of a small helicoïdal VAWT, with a specific focus
on its structural optimization, in order to maximize the power extracted from the wind.
A first prototype has been design using static finite element calculations in order to assess the resistance of the
blades when they are submitted to large centrifugal forces. The turbine has been tested at different wind velocities
in CSTB wind tunnel and large deflections of the blades have been observed at large velocities, leading to
initiation of cracks at the junction of arms and blades.


Main body of abstract

In order to optimize the geometry and material of the rotor, experimental tests have been carried out on
composite material coupons in order to measure mechanical characteristics of the chosen
laminate. Then, a complete large displacement finite element model has been developed using adapted behavior
laws and the rotor has been accelerated until its maximum in-service velocity. Time calculations have been performed
using the time integration explicit solver of LS-DYNA software. Evolution of stresses, strains and blade deflections
have been post-processed and compared to test observations. A good agreement has been obtained and the
model parameters have been re-used to optimize the rotor in order to build a second prototype. To
minimize the weight of the blades and the arms, sensitive parametric studies have then been realized on laminate
thickness, core and laminate materials characteristics and geometry of the arms. Finally, a carbone epoxy laminate has
been chosen and a second prototype has been build by foundation Ocean Vital. A second campaign of wind tunnel tests is planed in a
near future.

Conclusion

A non-linear finite element model able to simulate the structural behavior of a sandwich made vertical axis wind
turbine submitted to large acceleration has been developed and correlated with wind tunnel tests.
This model has been re-used to optimize the structural characteristics of the rotor with the objective to minimize
its weight and to build a second prototype which will be also tested in a near future. The authors want to thank the
Region Pays de la Loire for its fnancial support and all the partners of the Aerojoules project : Fondation Ocean Vital,
Garos, Jalais, AIC, CSTB and ICAM


Learning objectives
This presentation aims to demonstrate that nonlinear structural finite element simulation may be useful to tackle
the dynamic behavior of vertical axis wind turbine and to optimize the structural characteristics of the rotor.
A procedure to obtain realistic tension and bending characteristics of the laminate used for the rotor will be also
presented.