Numerical analyses and optimizations on the flow in the nacelle region of a wind turbine
2018
Abstract. The present study investigates flow dynamics in the hub region of a wind
turbine focusing on the influence of nacelle geometry on the root
aerodynamics by means of Reynolds averaged Navier–Stokes simulations with the
code FLOWer. The turbine considered is a generic version of the Enercon E44
converter incorporating blades with flat-back-profiled root sections. First, a
comparison is drawn between an isolated rotor assumption and a setup
including the baseline nacelle geometry in order to elaborate the basic flow
features of the blade root. It was found that the nacelle reduces the trailed
circulation of the root vortices and improves aerodynamic efficiency for
the inner portion of the rotor; on the other hand, it induces a complex
vortex system at the juncture to the blade that causes flow separation. The
origin of these effects is analyzed in detail. In a second step, the effects
of basic geometric parameters describing the nacelle have been analyzed with
the purpose of increasing the aerodynamic efficiency in the root region.
Therefore, three modification categories have been addressed: the first
alters the nacelle diameter, the second varies the blade position relative to
the nacelle and the third comprises modifications in the vicinity of the
blade–nacelle junction. The impact of the geometrical modifications on the
local flow physics are discussed and assessed with respect to aerodynamic
performance in the blade root region. It was found that increasing the
nacelle diameter deteriorates the root aerodynamics, since the flow
separation becomes more pronounced. Possible solutions identified to reduce the
flow separation are a shift of the blade in the direction of the rotation or the
installation of a fairing fillet in the junction between the blade and the
nacelle.
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