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Abstract: This paper treats the vortex shedding phenomenon of a savonius wind turbine, whose knowledge is primordial in correctly calculating the airloads on the blades. The specific aim being to numerically predict the disposition and geometry of the vortical structures in the wake of the savonius rotor whose existence has been visualised by a number of experimentalists. In the numerical approach, the blade is represented by discrete bound vortices while the wake is generated in a time stepping calculation as an emission of free vortices. The calculations are enhanced by the Newmann boundary condition coupled to the Kutta–Joukowsky condition and the Kelvin's theorem for the conservation of circulation. The convection of the vortices in the wake is accomplished through a predictor corrector integration scheme. A code has been developed which predicts the wake structure to be in good agreement with the experimental visualizations: For low tip speed ratios, the wake consists of a series of three discrete vortical structures while at higher tip speed ratios, the characteristic structure is the presences of a central vortex. [Copyright &y& Elsevier]

Presently, there exist few numerical methods which treat the inverse problem for the determination of the geometry of wind turbine blades. In this work, authors intend to solve the inverse optimum project for horizontal axis wind turbine in which the selection of the circulation distribution is obtained by resolving two variational problems: the first consists in sorting the circulation distribution on the lifting line, which, for a given power extracted by the wind turbine, minimizes the loses due to the induced velocity. In the second, the optimal circulation distribution is selected such that the kinetic energy of the wind downstream of the rotor disc is minimum, when the energy extracted by the wind turbine for one rotating period is imposed. A code has been developed which incorporates the real pitch of the helicoidal vortex wake. Very promising results have been obtained: the circulation distribution for a given extracted power and the chord lengths distribution law along the blade span. [ABSTRACT FROM AUTHOR]

Abstract: The aerodynamic characteristics of wind turbines are closely related to the geometry of their blades. The innovation and the technological development of wind turbine blades can be centred on two tendencies. The first is to improve the shape of existing blades; the second is to design new shapes of blades. The aspiration in the two cases is to achieve an optimal circulation and hence enhancing some more ambitious aerodynamic characteristics. This paper presents an inverse design procedure, which can be adapted to both thin and thick wind turbine blade sections aiming to optimise the geometry for a prescribed distribution of bound vortices. A method for simulating the initial contour of the blade section is exposed, which simultaneously satisfy the aerodynamic and geometrical constraints under nominal conditions. A detailed definition of the function characterising the bound vortex distribution is presented. The inviscid velocity field and potential function distributions are obtained by the singularities method. In the design method implemented, these distributions and the circulation of bound vortices on the camber line of the blade profile, are used to rectify its camber in an iterative calculation leading to the final and optimal form of the blade section once convergence is attained. The scheme proposed has been used to design the entire blade of the wind turbine for a given span-wise distribution of bound circulation around the blade contour. [Copyright &y& Elsevier]