A damage assessment for wind turbine blades from heavy atmospheric particles

A numerical study of how to simulate heavy atmospheric particle collisions with a 38-m, 1.5-MW horizontal axis wind turbine blade is discussed. Two types of particles were considered, namely hailstones and rain drops. Computations were performed by using a two-dimensional inviscid flowfield solver along with a particle position predictor code. Three blade sections were considered: at 35% span and characterized by a DU 97-W-300 airfoil, at 70% span with a DU 96-W-212 airfoil, and at 90% span using a DU 96-W-180 airfoil. The three blade sections are constituted by 8-ply carbon/ epoxy panels, coated with ultra-high molecular weight polyethylene (UHMWPE). Hailstone and raindrop simulations were performed to estimate the location of the striking occurrences and the blade surface area subject to damage. Results show that the impact locations along the blade are a function of airfoil angle of attack, local relative velocity, airfoil shape, aerodynamics and mass of the particle. Hailstones were found to collide on nearly every portion of the blade section along their trajectory due to their insensitivity to the blade flowfield. The damaged surface areas were found to be small when compared to the overall impingement surface, and most of delamination damage was localized on the blade leading edge. Moreover, panel delamination occurred for outboard sections, when r=R ≥ 0.90. The damage due to raindrops was divided in an erosive and a fatigue contribution due to the impact force. It was observed that the erosive damage follows the cubic power of the blade velocity, whereas the impact force follows the square power of the blade velocity. Moreover, it was seen that the rain drops are sensitive to the blade flowfield, due to shape modifications through theWeber number. In particular, a sensitive behavior of the damage with respect to the blade angle of attack was observed.