The performance of wind turbines is significantly affected by the atmospheric condition of their operating environment. Because rain is a common phenomenon in many parts of the world, understanding its effect on the performance of wind turbines provides valuable information in determining the site for a new wind farm. We developed a multiphase computational fluid dynamics (CFD) model to estimate the effect of rain by simulating the actual physical process of rain droplets forming a water layer over the blades by coupling the Lagrangian Discrete Phase Model (DPM) and the Eulerian Volume of Fluid (VOF) models. We applied our model to a wind-turbine blade airfoil and studied the effect of rain for different rainfall rates in addition to the effect of surface tension and surface property of the airfoil. We observed that, at low rainfall rates, the performance of the airfoil is highly sensitive to the rainfall rate. However, if the rainfall rate is high enough to immerse most of the airfoil surface under water, a further increase in the rainfall rate does not have a substantial effect on the performance of the airfoil. (C) 2016 Elsevier Ltd. All rights reserved.