Computational analysis of shrouded wind turbine configurations using a 3-dimensional RANS solver

The use of a shroud is known to improve performance. In this work, the flow physics and performance of shrouded turbines is assessed by solving the Reynolds Averaged Navier-Stokes equations supplemented with a transition model. Shroud geometries are evaluated for their augmentation of mass flow through the turbine. Initial assessments are performed using axisymmetric calculations of annular wings with high-lift airfoils as cross sections. The mass flow amplification factor is defined as a performance parameter and is found to increase nearly linearly with radial lift force. From a selection of considered airfoils, the Selig S1223 high-lift airfoil is found to best promote mass flow rate. Full three-dimensional simulations of shrouded wind turbines are performed for selected shroud geometries. The results are compared to open turbine solutions. Augmentation ratios of up to 1.9 are achieved. Peak augmentation occurs at the highest wind speed for which the flow over the blade stays attached. Flowfields are examined in detail and the following aspects are investigated: regions with flow separation, the development of velocity profiles, and the interaction between the turbine wake and shroud boundary layer. The sensitivity of the solutions to rotation rate is examined.