Loads calculation for wind turbine design under the influence of rain

This work investigates the impact of rain on the power production of a wind turbine, including structural flexibility effects. Wind turbines are subjected to numerous conditions, including the change of weather, such as snow, hail and rain. In the available literature, the main focus has been given to the effects of snow rather than rain. In this study, a strong one–way fluid–structure interaction (FSI) approach was utilised to investigate the interconnected characteristics of the fluid and structural domains. The Reynolds-averaged Navier–Stokes (RANS) approach incorporated with multiple reference frame (MRF), discrete phase modelling (DPM) and wall–film model were used to investigate the aerodynamic behaviour of the selected geometries. The NACA 0012 and S809 aerofoils were used as the validation test cases, and then similar methodology was applied for the NREL Phase VI wind turbine. The structural response of the wind turbine was accounted by a three dimensional finite element method (FEM) utilising the shell theory. Parametric studies are included in this work to analyse the effect of rain characteristics towards the surrounding airflow. It was found that the presence of rain negatively affected the aerodynamics of these selected geometries, measured in terms of lift, drag and torque production. For the NREL Phase VI wind turbine, a maximum torque reduction by 19.97% was obtained when the freestream velocity was varied. The aerodynamic penalties were more evident by increasing the rainfall rate up to 18.0% drop of torque respectively from rainfall rate of 3.75 g/m3 to 30.0 g/m3. Nonetheless, higher torque production was found for larger raindrop diameter. An increase by 11.27% of torque was observed when the diameter is increased from 3 mm to 6 mm. In terms of structural response, the thrust showed a dominant influence. Additionally, the amount of the total deformation was dominated by the z deformation in the direction of the thrust. The blades deflections were found between 3.71% and 27.30%, measured in terms of total deflections. Both blades experienced different amount of deformation because they depended on the intensity of the rain droplets at their vicinity, due to the behaviour of the rain particles. Then, the associated stress analysis of the wind turbine was measured in term of von–Mises stress. Similarly, higher von-Mises stress was recorded for the rainy case than the dry condition. As a conclusion, the presence of rain has detrimental effects on the aerodynamic and structural characteristics of a wind turbine