Oscillating Water Column Wave Energy Converter for Low Wave Height Conditions

Abstract

For continuous and uninterrupted extraction of energy from marine wave motion, majority of wave energy extraction systems employ bi-directional turbines. The aerodynamic loss due to symmetrical placement of guide vanes causes a major loss in power output of the system. To optimize this problem, researchers have developed and tested a variety of oscillating water column air turbines. Most commonly used are the axial turbines because of their simplicity and operational ease. The present work focuses upon design of an oscillating water column energy extraction system based on uni-directional axial impulse turbine with a novel rectifying system arrangement which primarily focuses to minimize the losses due to downstream guide vanes and in turn shoot up the power output for low wave height conditions. A numerical model was developed and investigated using RANS equations and k-omega SST turbulence model. The results obtained portrays that the proposed flap based bi-directional impulse system is operationally viable and produces substantially greater power output in comparison to conventional bi-directional and uni-directional turbine systems under low wave height conditions. A hybrid choking scheme was followed which resulted in additional power output. Results show that full choking of the idle turbine is ensured during the inhalation cycle, which was not possible in existing models. During the exhalation cycle, additional power output was also obtained from the secondary turbine i.e., front end turbine during exhalation cycle. The proposed system generates maximum total power output at around flow coefficient of 1.