TITLE:
A Counter-Rotating Impulse Turbine for Wave Energy Conversion
AUTHORS:
Manabu Takao, Kohei Yamada, Shinya Okuhara, M. M. Ashraful Alam, Yoichi Kinoue, Toshiaki Setoguchi
KEYWORDS:
Air Turbine, CFD, Fluid Machinery, Oscillating Water Column (OWC), Wave Energy Conversion
JOURNAL NAME:
Open Journal of Fluid Dynamics,
Vol.8 No.4,
December
24,
2018
ABSTRACT: Wave energy can be converted to the electrical energy by using a wave energy
converter. The wave energy converter with oscillating water column (OWC)
is one of the most promising devices because of its simple structure and easy
maintenance. In this device, an oscillating water column due to the wave motion
is used to drive an air column. An air turbine is used to convert the
pneumatic energy of this bi-directional airflow into the mechanical energy.
The counter-rotating impulse turbine for wave energy conversion has been
proposed and tested so far, and the average efficiency has been shown to
about 0.3. On the contrary, in another offshore experiment, it has been reported
that the power generation efficiency of this turbine is larger than Wells
turbine in case of small waves. However, there is a scarcity of the detailed
characteristics data of counter-rotating impulse turbine. In a previous study,
the authors investigated the effect of rotor blade solidity and setting angle of
guide vane on the performance of this turbine, and they clarified that the efficiency
of this turbine is higher than impulse turbine with single rotor in the
range of high flow coefficients. The present study aimed to investigate the effect
of rotor blade profile on the turbine performance by using the computation
fluid dynamic (CFD) analysis. The inner and outer angles of turbine rotor
blade are changed in the range of 50° to 70°. The commercial CFD software
of SCRYU/Tetra of Cradle Co. Ltd. was used in the present work. The
Reynolds averaged Navier-Stokes (RANS) equations were used as the governing
equations and the low Reynold’s number SST k-ω model was used to
predict the turbulent stresses. As a result, it was found that the inner angle of γ = 70° and the outer angle of γ = 60° of the turbine rotor blades can give the best turbine efficiency and it shows the efficiency close to the impulse turbine
with single rotor, even in the range of low flow coefficients.