Simulation of Damage Progression on Wind Turbine Blades Subject to Particle Erosion

A time-marching code for predicting the evolving shape of wind turbine airfoils subject to erosion is discussed. The erosive damage to the blade surface was represented by sand grains colliding with the blade leading edge. The erosion rate was computed on the airfoil, and the damage depth was evaluated at each location. It was found that the locations of maximum erosion rate did not necessarily overlap with the locations of maximum eroded depth on the blade surface. In particular, the maximum damage depth was found very near the leading edge, and the results are in good agreement with photographic evidence. Three main phases were identified through the blade lifespan: an upper core breach, a lower core breach, and a leading edge core breach. A parametric study was performed in order to determine the most relevant drivers of the blade lifespan. In particular, the sand grain diameter was found to be the most significant driver, and the lifespan of the blade decreases parabolically as the grain diameter increases. Both the blade lift coefficient and the turbine hub height showed a direct relationship with blade lifespan. Large lift coefficients and large turbine hub heights are beneficial to increasing blade lifespan. It was also found that modern, large wind turbines are affected consistently less by sand erosion than small wind turbines. Such an effect is due to the increased influence of the blade flowfield toward a deviation of the incoming particles when large blade chord lengths are involved. Finally, a survey of various airfoil geometries allowed to identify the shape of the leading edge along with the airfoil aft camber as the primary drivers of blade section lifespan. The survey was performed by using the NREL S-airfoil family along with the tip-region airfoil DU 96-W-180. It was found that bulbous and round leading edges, coupled with moderately aft-cambered airfoils allowed for the longest blade lifespans, since they reduce the blade upper suction peak and offer steeper impact angles to the particles.