The physical modelling and aerodynamics of turbulent flows around horizontal axis wind turbines Sherwan A. Abdulqadir * , Hector Iacovides, Adel Nasser Turbulence Mechanics Group, School of MACE, University of Manchester, Manchester, UK article info Article history: Received 12 August 2016 Received in revised form 2 November 2016 Accepted 8 November 2016 Available online xxx Keywords: Computational fluid dynamics Wind turbine aerodynamics Unsteady RANS Turbulence modelling abstract This paper aims to assess the reliability of turbulence models in predicting the flow fields around the horizontal axis wind turbine (HAWT) rotor blades and also to improve our understanding of the aero- dynamics of the flow field around the blades. The simulations are validated against data from the NREL/ NASA Phase VI wind turbine experiments. The simulations encompass the use of twelve turbulence models. The numerical procedure is based on the finite-volume discretization of the 3D unsteady Reynolds-Averaged Navier-Stokes equations. The resulting simulations are compared with the full range of experimental data available for this case. The main contributions of this study are in establishing which RANS models can produce quantita- tively reliable simulations of wind turbine flows and in presenting the flow evolution over a range of operating conditions. At low (relative to the blade tip speed) wind speeds the flow over the blade sur- faces remains attached and all RANS models tested return the correct values of key performance co- efficients. At higher wind speeds there is circumferential flow separation over the downwind surface of the blade, Moreover, within the separation bubble the centrifugal force pumps the flow outwards, which at the higher wind speeds suppresses the formation of the classical tip vortices. RANS models which do not rely on the linear effective viscosity approximation generally lead to more reliable predictions at higher wind speeds. By contrast some popular linear effective viscosity models perform the poorest over this complex flow range. Finally all RANS models are also able to predict the dominant (lowest) frequency of the pressure fluctuations. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Renewable sources of energy (such as wind, solar and wave) continue to attract tremendous interest because of the negative environmental impact of the traditional energy sources that are based on fossil fuels, such as coal, oil and natural gas. One of the most developed and cost-effective renewable energy sources is wind energy, because of its environmentally friendly and economically low cost. The global cumulative capacity of wind power installations approached 198 GW in 2010, while this ca- pacity increased dramatically to reach to 370 GW by the end of 2014 [1]. This demand has speeded up the development of wind turbine technologies. The Horizontal Axis Wind Turbine (HAWT) emerged as the most popular in today's market, because of its high efficiency. Numerous efforts have been directed towards the improvement of the design of wind turbines and the efficiency of the rotor blades. Early investigations relied mainly on the use of the Blade Element Momentum (BEM) approaches and the experimental data for lift and drag coefficients to investigate the complex flow around the blade [2e4]. BEM approaches fail to resolve the 3D flow around the rotor blade because they use 2D airfoil data and empirical models to capture the 3D influences [5]. Moreover these models are limited by impractical assumptions such as uniform wind and steady flow [6]. Although the data measurements are able to provide precise and reliable performance parameters of the wind turbine, the interior details of the flow around the blade remain unexplored. Consequently, the development of more effective designs remains a slow process based on trial and error. Therefore to overcome the restrictions of the experimental methodology, the current study employs computational fluid dynamics (CFD) simulations to * Corresponding author. E-mail addresses: sherwan.abdulqadir@manchester.ac.uk, sherwan_j@yahoo.co. uk (S.A. Abdulqadir). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2016.11.060 0360-5442/© 2016 Elsevier Ltd. All rights reserved. Energy xxx (2016) 1e33 Please cite this article in press as: Abdulqadir SA, et al., The physical modelling and aerodynamics of turbulent flows around horizontal axis wind turbines, Energy (2016), http://dx.doi.org/10.1016/j.energy.2016.11.060