A Numerical Study On The Performance Of Diffuser For A New Tidal Turbine

Tidal current energy is one of the most important ocean renewable energies,which can be utilized by a tidal current turbine.Comparing with solar power generation and wind power generation,the power output by tidal power generation is predictable because the tidal current is periodic and is not affected by the weather.Conventional tidal current turbine has the problem of high installing and maintenance cost because it is installed at bottom of the sea.This is one of the biggest obstacles in implementation of the tidal current power generation.To solve the high cost problem,a new tidal power generation concept,the floating type diffuser augmented tidal current turbine,has been proposed and a feasibility study on this new concept has been carried out(Obara,2017)in our laboratory.In this study,as a continuation of the previous research,I focus on optimization of the diffuser shape.Particularly I want to find the influence of the diffuser thickness on the flow velocity increase inside the diffuser and the drag force on the diffuser by using CFD simulation.OpenFOAM is used for the numerical simulation.Three diffuser models with different thickness are considered.Numerical simulations are performed on the three diffuser models without turbine under different inflow velocities.The results of velocity distribution,drag coefficient,streamline,vorticity and pressure distribution are compared among the three diffuser models and the effect of diffuser thickness on the performance of the tidal current turbine is discussed.Finally,a numerical simulation on a diffuser augmented turbine model is carried out to examine the effect of the turbine rotation.