Unsteady Aerodynamic Simulation of Offshore Wind Turbines with Overset Grid Technology

Wind energy, which is renewable and sustainable, represents a potential to solve the energy and environment crisis, especially for the coastal countries which have enormous ocean wind energy resource. With special and strong advantages over onshore wind turbines, offshore wind turbines (OWT) become more and more attractive. Compared with traditional onshore wind turbines, the environment loads on OWTs are more complex. Due to wave-wind interaction, the wind speed distribution above free surface differs from that on land. Accurate aerodynamic prediction in unsteady and non-uniform inflow wind is one of the common challenges in design of offshore wind turbines. The aerodynamic simulation of an offshore wind turbine, the NREL-5MW baseline wind turbine, is conducted. The three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations are solved for the aerodynamic numerical simulation. The naoe-FOAM-os-SJTU solver, which is based on OpenFOAM and overset grid technology, is employed. The aerodynamic simulation of the NREL-5MW baseline wind turbine under steady and uniform inflow wind is first conducted. And the unsteady aerodynamic simulation of the wind turbine under unsteady and non-uniform inflow wind is done. With numerical simulations, the time series of the torque and thrust of the wind turbine are obtained, together with the detailed information of the wake flow field, and the limiting streamline of the blade surface and the pressure coefficient distribution in different cross-section are also available to clarity the detailed flow filed information. The comparison of results from numerical simulation in different inflow wind conditions is carried out, and the effect of the wave-wind interaction on the unsteady aerodynamic performance of offshore wind turbine is studied. With careful analysis of the numerical results, proper discussions and conclusions are made.