Modelling & Dynamic Analysis of Wind Turbine Blades

Abstract

Wind turbine blade is one of the important components requiring more attention at the design stage.These blades are made up of fibrous material and sometimes hollow composite web sections may be employed in its construction. The main focus in its design is to achieve a desired strength to withstand various loads as per the power requirements. In view of this, modelling & dynamic analysis of blades is an essential requirement not only to avoid resonant vibrations but also to understand the stability of operation during various operating conditions. In this line, present work focuses on dynamics of horizontal-axis wind turbine blade with NACA 63415 profiles subjected to aerodynamic, centrifugal and gravity loads.The basic geometrical parameters of the blade are designed by using blade element moment method & the blade is modelled as a ruled 3D surface. By computing element wise cross sectional details from 3D model, a 1D beam finite element modelling is developed and modal characteristics are obtained. These are further validated with 3D finite element model result. Then, the effects of the tip speed ratio and rotational speed on the natural frequencies are studied.Further, finite element model have 10 elements with 6 degrees of freedom per node is used to obtain the dynamic response of the blade subjected to various loading conditions. The effect of aerodynamic, centrifugal and gravity parameters on the frequency response, edge -wise and flap-wise beating at the tip of blade are studied. The iterative programs developed in the work helps in testing the blade frequencies & response at any operating conditions.In order to estimate the stability during rotation, the frequency responses are obtained from response histories at the blade tip, by using Fast Fourier Transform algorithm.It is found that the centrifugal loads have profound effect on the frequency responses compared with other loads. The dynamics of long blade when rotating at varying wind conditions (aerodynamic loads) is influenced by gravity loads also.