Wave-Current Interactions in a Marine Current Turbine Using ANSYS FLUENT CFD

Abstract

This paper presents the results of the study on the wavecurrent interactions of an idealized full scale marine current turbine (MCT). A multi-phase flow model is used for simulation of three cases: still water and two different wave heights. The Standard k-ω turbulence model is chosen based on the stability of the pressure and velocity plots upstream and downstream the turbine rotor plane. The three cases are used in the present study to compare the effects of wave height and current velocity on the turbine rotor. The velocity, and pressures on the turbine blades are computed for each case using ANSYS FLUENT CFD Software. The thrust, torque, and power in the MCT are calculated using the results obtained from the CFD simulation. The turbine rotor blades are drafted in 3D using SolidWorks by extruding cross sections of a 43.2 m diameter turbine blade published by the National Renewable Energy Laboratory (NREL). Tetrahedral mesh elements are used to represent the multiphase fluid domain and rotor blades in ANSYS ICEM CFD due to its simplicity and speed of computation. The ANSYS FLUENT simulation is set up to run air and water phases in the domain, while the rotor blade is suspended in the fluid domain, such that there is 20 m of water in front and 100 m behind the plane of rotation. The effects of varying wave heights on the thrust, torque, and power are presented based on the tip speed ratios. The power generated by the turbine rotor from the wave cases is found to be higher than those for the still water case, at lower current velocities. However, at current velocities higher than 2.00 m/s, the power generated from the still water case is higher than the wave cases. At lower tip speed ratios, the thrust on the turbine, subjected to wave conditions, is lower than that for the still water condition. At higher tip speed ratios, the thrust on the turbine, under wave conditions, is higher than that for the still water condition. The torque decreases exponentially with increases in the tip speed ratio for all three cases, but the torque remains nearly constant with increases in wave height. The results provide detailed information which would be valuable in the design and operation of marine current turbines in wave environments.