Vortex Dynamics in the Wake of Three Generic Types of Freestream Turbines

Abstract

An analysis of the vortex dynamics in the wake of three different freestream turbine concepts is conducted to gain a better understanding of the main processes affecting the energy recovery in their wakes. The turbine technologies considered are the axial-flow turbine (AFT), the crossflow turbine (CFT), also known as the H-Darrieus turbine, and the oscillating-foil turbine (OFT). The analysis is performed on single turbines facing a uniform oncoming flow and operating near their optimal efficiency conditions at a Reynolds number of 107. Three-dimensional (3D) delayed detached-eddy simulations (DDES) are carried out using a commercial finite volume Navier–Stokes solver. It is found that the wake dynamics of the AFT is significantly affected by the triggering of an instability, while that of the CFT and the OFT are mainly governed by the mean flow field stemming from the tip vortices' induction.