The influence of time step setting on the CFD simulation result of vertical axis tidal current turbine

This paper investigates the influence of time step setting on the CFD simulation result of vertical axis tidal current turbine. Two main features of time step setting have been studied. The first feature concerns with time step size setting that representing the detailed calculation on each degree in one turbine rotation. The second feature deals with number of time step setting that representing how many turbine rotations need for achieving steadiness results. In this study, two-dimensional (2D) analysis of Computational Fluid Dynamics (CFD) simulation using ANSYS-Fluent code with Sliding Mesh technique is used to solve the incompressible Unsteady Reynolds Averaged Navier-Stokes equations. The finite volume discretization method with second-order scheme and the SIMPLE algorithm are used for all transport equations. Firstly, the numerical model has been validated with available experimental data. Some given scenarios of time step setting for vertical axis tidal turbine have been modeled subsequently. Several increment angle (1 degrees, 5 degrees, 10 degrees and 20 degrees) are investigated and chosen the best value of them. Afterwards, the best increment angle combining with several number of rotations (2, 4, 6 and 8 rotations) are investigated. The results show that the more specific of time step size has the better result but it needs more computational times. The recommendation of time step size is 5 degrees up to 1 degrees. The steadiness calculation result is achieved at six turbine rotations and the rest has no significant effect.