142 J SCI IND RES VOL 69 FEBRUARY 2010 *Author for correspondence E-mail: slain@uao.edu.co Aeromechanical evaluation of large HAWT’s blades S Lain 1* , B Quintero 1 and Y U López 2 1 FMRG, 2 GIEN, Energetics and Mechanics Department, Universidad Autónoma de Occidente, Cali, Colombia Received 12 June 2009; revised 03 December 2009; accepted 04 December 2009 This paper presents aeromechanical evaluation of a blade (length, 50 m) of horizontal axis wind turbines (HAWT). Aerodynamic module combines three-dimensional non-linear lifting surface theory approach and a two-dimensional panel method for steady axisymmetric flow. It provides effective incident velocity and angle of attack at each blade section and 3D pressure distribution on blade as an input data for finite element analysis (FEA) package. FEA provides deformations, strains and stress distributions along blade and material induced fatigue. Degradation linear accumulation model was used in fatigue study under one million cycles of loading. Calculated accumulated damage was found below critical value. Keywords: Aerodynamics, Numerical simulation, Structural behaviour, Wind turbine Introduction In normal running, blades of a wind turbine must withstand centrifugal forces, bending moments caused by pressure aerodynamic forces and gyroscopic effects. In order to improve design of horizontal axis wind turbine (HAWT) blades, optimisation of design requires more accurate estimations of loads and therefore more elaborate models incorporating coupling of aerodynamics, structural dynamics and wind turbulence. Modern HAWT blades are composite thin structures with a rather sophisticated distribution of laminated resins spanwise and chordwise. Mechanical optimisation of such devices should be made by modelling blade as a set of thin layer elements rather than using beam elements approach. Accurate evaluation of interlaminar strengths require a detailed evaluation of the external force field, namely pressure field, which is supposed to supply a better estimate of rotor performance than simplified momentum theories, using global lift and drag forces at each section. This paper presents a combination of aerodynamic module, based on Lifting Surface method (LSM) and 2D panel method, and structural module, based on ANSYS finite element package, which is applied to analyse a large HAWT 1 (blade length, 50 m; and rated power, 3 MW). Aerodynamic Analysis Proposed configuration wind turbine modeled by LSM is a steady, uniform wind that flows over a HAWT with K blades of radius R, rotating at constant angular velocity ω aligned with incoming free stream velocity, V ∞ . A Cartesian system of coordinates (X, Y, Z) is defined relative to first blade (Fig. 1). Y direction coincides with turbine rotation axis, oriented towards incoming wind stream. Z axis goes along blade span, oriented from root to tip and starting at hub pitching centre. X direction is third orthogonal right-handed axis lying on rotation plane. Absolute non-stationary irrotational velocity field is computed in terms of upstream velocity, V ∞ , plus a perturbation due to velocities induced by vorticity field. It is assumed that vorticity is concentrated at thin blade boundary layers and wakes, modelled as vorticity sheets (Fig. 1). Vorticity associated to boundary layers can be merged into a single vortex surface, the lifting surface. LSM geometry is a cambered twisted continuous surface build up by the sequence of profile cambered middle lines going from leading edge to trailing edge 2 . LSM allows obtaining an effective velocity and angle of attack at each section of blade 3 . Journal of Scientific & Industrial Research Vol. 69, February 2010, pp. 142-145