Abstract
The cost effectiveness of a tidal stream turbine
can be improved by maximising the power extracted for a
given rotor diameter. This paper presents a numerical and
experimental study showing that winglets could be used
to this end. The numerical simulations were conducted
using Tornado, a vortex lattice code, which can model
the interaction between different spanwise sections unlike
Blade Element Momentum methods. Tornado was used to
identify the important winglet design parameters such as
dihedral angle. Three metrics were used to evaluate the
designs: power coefficient, hydrodynamic efficiency and
structural efficiency, thus assessing their effectiveness not
only in relation to power extraction but also to the blade
material cost per kilowatt. It was found that the three
metrics give different optimum winglet designs. Tornado
cannot capture viscous effects and so an experimental study
was conducted on four designs. These were tested on a
small-scale horizontal axis turbine in the Ifremer flume
tank. In all tests, the pressure side winglets offered an
improvement in performance over the datum case, though
the hydrodynamic failure was more abrupt at low tipspeed
ratios. The suction surface winglets were inferior
to the datum design. The impact of winglets on the blade
spanwise flow was found to have a significant effect on
the amount of loss generated due to secondary kinetic
energy in the wake. The importance of spanwise flow in
determining turbine performance highlights the need for
fully 3D blade design codes. The inviscid code used in this
paper could complement existing quasi-3D design tools.
can be improved by maximising the power extracted for a
given rotor diameter. This paper presents a numerical and
experimental study showing that winglets could be used
to this end. The numerical simulations were conducted
using Tornado, a vortex lattice code, which can model
the interaction between different spanwise sections unlike
Blade Element Momentum methods. Tornado was used to
identify the important winglet design parameters such as
dihedral angle. Three metrics were used to evaluate the
designs: power coefficient, hydrodynamic efficiency and
structural efficiency, thus assessing their effectiveness not
only in relation to power extraction but also to the blade
material cost per kilowatt. It was found that the three
metrics give different optimum winglet designs. Tornado
cannot capture viscous effects and so an experimental study
was conducted on four designs. These were tested on a
small-scale horizontal axis turbine in the Ifremer flume
tank. In all tests, the pressure side winglets offered an
improvement in performance over the datum case, though
the hydrodynamic failure was more abrupt at low tipspeed
ratios. The suction surface winglets were inferior
to the datum design. The impact of winglets on the blade
spanwise flow was found to have a significant effect on
the amount of loss generated due to secondary kinetic
energy in the wake. The importance of spanwise flow in
determining turbine performance highlights the need for
fully 3D blade design codes. The inviscid code used in this
paper could complement existing quasi-3D design tools.
| Original language | English |
|---|---|
| Publication status | Published - 1 Sept 2019 |