WIND ENERGY Wind Energ. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/we.535 RESEARCH ARTICLE Wind turbine performance in shear flow and in the wake of another turbine through high fidelity numerical simulations with moving mesh technique Joseph Seydel and Alberto Aliseda Department of Mechanical Engineering, University of Washington, Seattle, Washington, 98195-2600, USA ABSTRACT We present numerical simulations of two horizontal axis wind turbines, one operating under the wake of the other, under an incoming sheared velocity profile. We use a moving mesh technique to represent the rotation of the turbine blades and solve the unsteady Reynolds averaged Navier–Stokes equations with a shear stress transport k  ! turbulence model. Temporal evolution of the lift and drag coefficients of the front turbine show a phase shift in the periodic cycle due to the non-uniform incoming free stream velocity. Comparisons of the lift and drag coefficients for the back turbine with the unperturbed behaviour of the front demonstrate the complex non-linear interactions of the blades with the wake, with a sig- nificant decrease in overall performance and two peaks at specific points in the cycle associated with local angle of attack modification in the wake. The vorticity field in the near wake shows tilting of the vortex lines in the wake due to the shear and a faster diffusion of the tip vortical signature compared with the uniform free stream velocity case. Observations of the wake–wake interaction show good agreement with recent studies that use different methodologies. Copyright © 2012 John Wiley & Sons, Ltd. KEYWORDS wind energy; turbulent wake; turbine–wake interaction; shear flow Correspondence Alberto Aliseda, Department of Mechanical Engineering, University of Washington, 4000 15th Ave NE Box 352600, Seattle, Washington 98195-2600, USA. E-mail: aaliseda@u.washington.edu Received 11 November 2010; Revised 8 September 2011;Accepted 15 September 2011 1. INTRODUCTION As energy consumption increases and non-renewable energy sources are depleted, the need for clean renewable energy sources is continually increasing. Solar, wind, wave and tidal energy are all renewable sources that can contribute to the overall reduction in dependence on non-renewable fossil fuels. Wind energy has emerged as one of the leading technolo- gies in providing cost-effective non-polluting renewable energy. However, wind power is still relatively expensive compared with non-renewable sources such as coal, despite reducing the cost per kWh by a factor of 10 over the past 20 years. More- over, the widespread deployment of wind turbine farms is leading to an exhaustion of the prime sites, especially in small, highly technologically advanced countries in Western Europe. To further reduce the cost of wind energy and improve its availability as a non-polluting energy source, improvements in wind farm site optimization are necessary. Further under- standing of the interactions between wind turbines and wakes from turbines located upwind from them is key to improving the utilization of the wind resource and raising the efficiency of installed turbines. In the last 30 years of rapid development, turbine designers have improved energy output by reaching higher into the atmospheric boundary layer and capturing more consistent and higher speed winds. With the increased height has come increased weight. If blade design is scaled up to maintain stiffness, blade weight increases with the blade length cubed, whereas the energy capture increases with the blade length squared. 1 To make wind turbines that are economically viable, weight reductions are required. The drawback arises from the combination of increased span and decreased weight resulting in turbines that are more dynamically active than their predecessors. The dynamic response of operating wind turbines to inflow turbulence can lead to structural fatigue and, ultimately, to failure. Inlet flow turbulence in wind turbines is most commonly generated by atmospheric phenomena Copyright © 2012 John Wiley & Sons, Ltd.