Thermal Analysis of the Nacelle of a Small Horizontal Axis Wind Turbine Using a CFD Model in ANSYS-FLUENT

Abstract

Horizontal Axis Wind Turbines (HAWT-s) are the most commonly used wind turbines all over the world in the sector of renewable energy. Apart from the blades, the nacelle is an important part of HAWT-s, which houses the electromechanical equipment. However, the nacelle being a closed chamber, mostly sealed from the outside, is prone to temperature increase due to the heat generated by the drivetrain, brake and, most significantly, generator. Commercial, high-capacity HAWT-s employ “forced cooling” systems to tackle this issue and published literature indicates the application of computational fluid dynamics (CFD) software packages in studying the effectiveness of the cooling techniques for the nacelles of such turbines. For small-capacity, low-cost HAWT-s meant for community level power supply, the cooling of the nacelle may be effected by a zero-cost natural ventilation system in the form of a pair of air vents on the windward and leeward sides, that is, the front and rear faces of the nacelle respectively, through which a draft of air is allowed to pass for cooling the nacelle components. However, CFD analysis for such systems have so far gone unreported, and this study aims at filling up the gap by making use of the software package ANSYS FLUENT (student version) for predicting the air flow pattern and temperature variations within the nacelle and evaluating the effectiveness of the air vents in keeping the temperatures sufficiently in check. It must be emphasized that the CFD studies reported in literature for larger wind turbines have mostly been demonstrated for two-dimensional computation domains considering only the space inside the nacelle body. The present work goes a step further considering a larger three-dimensional computation domain encompassing the space bounded by the nacelle, and connecting the two through the pair of air vents. This helps in simulating the free stream of air outside the nacelle and also helps in modelling the draft of air entering the nacelle through its front and leaving from behind. The simulation results indicate that the temperature does not reach very high values in the region from 0.2 to 0.4 m above the bottom of the nacelle, considering the nacelle to have a height of 0.41 m. This region, therefore, is suitable for the placement the electronic equipment necessary to control the wind turbine movements and operation. This work also reveals that the natural cooling attained by the draft of outside air directed into the nacelle is able to maintain the temperature in the nacelle well within the acceptable limits. The provision of circulation vents of suitable diameter on the front and rear faces of the nacelle, therefore, could provide a low cost solution to the cooling mechanism of the nacelle in small HAWTs.