This study presents full transient numerical simulations of a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type) with particular emphasis on the analysis of hydrodynamic characteristics. Turbine design and performance are studied using a time-accurate Reynolds-averaged Navier–Stokes commercial solver. A physical transient rotor-stator model with a sliding mesh technique is used to capture changes in flow field at a particular time step. A shear stress transport k-ω turbulence model was initially employed to model turbulent features of the flow. Two dimensional simulations are used to parametrically study the influence of selected geometrical parameters of the airfoil (camber, thickness, and symmetry-asymmetry) on the performance prediction (torque and force coefficients) of the turbine. As a result, torque increases with blade thickness-to-chord ratio up to 15% and camber reduces the average load in the turbine shaft. Additionally, the influence of blockage ratio, profile trailing edge geometry, and selected turbulence models on the turbine performance prediction is investigated.

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The present study discusses two-dimensional numerical simulations of a cross-flow vertical-axis marine (Water) turbine (straight-bladed Darrieus type) with particular emphasis on the turbine unsteady behavior. Numerical investigations of a model turbine were undertaken using commercial computational solvers. The domain and mesh were generated using a glyph script in POINTWISE-GRIDGEN, while the simulations were performed in ANSYS-FLUENT v14. For the simulation, a sliding mesh technique was used in order to model the rotation of the turbine; a shear stress transport k-! turbulence model was used to model the turbulent flow. In order to simulate the interaction between the dynamics of the flow and the Rigid Body Dynamics (RBD) of the turbine a User Define Function (UDF) was generated. The primary turbine operational variables of interest were the evolution of torque, power, and runaway speed. Numerical results show that as the freestream velocity is increased, the runaway angular speed of the turbine increases, which is consistent with the observation that the frequency of oscillation of the angular velocity (in the quasi steady-state) increases as the freestream velocity also increases. For a given turbine, it was observed that the increment in the moment of inertia of the turbine does not influence the average value of the runaway angular velocity (quasi-steady state) but causes an increase in the time taken for achieving this quasi steady-state.