Lift enhancement and drag reduction of lifting blades through the use of end-plates and detached end-plates

Abstract

Three-dimensional steady-state RANS simulations of the flow around a stationary finite-span blade have been carried out. The analysis is directed toward the vorticity dynamics, the forces acting on the blade and their spanwise distributions when using end-plates or detached end-plates, namely end-plates that are not in contact with the blade tips. The objective is to understand the physics at play in the vicinity of the blade tips with an emphasis on the detached end-plates, as the use of such devices could be beneficial for optimizing the performance of vertical-axis turbines. This paper also aims at providing simple guidelines regarding the use of end plates and detached end-plates. The results show that the presence of detached end-plates leads to an important increase of the blade lift coefficient in addition to a significant reduction of its drag coefficient. This is explained by the fact that the detached end-plates modify the path of the vorticity lines shed by the blade, thus affecting the vorticity distribution and the resulting circulation along the blade. This work also shows that the forces on the blade are more sensitive to the dimensions of the detached end-plates in the transverse direction than to any other geometric parameter.