Synthetic eddy generation and modelling of turbine operation in a turbulent tidal flow

Abstract--This paper presents an original computational methodology to simulate the operation of hydrokinetic turbines in turbulent onset flows. Turbulent eddies are generated in the flow by volume forcing terms in the Navier�Stokes equations, and the intensity of the result- ing turbulent stream is controlled to match prescribed conditions. The Navier�Stokes equations are numerically solved by a hybrid viscous/inviscid formulation in which a Boundary Integral Equation Method (BIEM) is used to predict the perturbation induced by a turbine, whereas the surrounding viscous flow is described by Detached Eddy Simulation (DES). The methodology is applied to simulate the operation of a horizontal�axis turbine in a 16% turbulent onset flow. The numerical results show that a divergence�free, nearly isotropic turbulent flow is established with a turbulence intensity 19% lower than the imposed value. Turbine loads are evaluated to quantify the effects of incoming eddies on device performance. By taking into account the velocity defect induced by the turbulence generation forcing terms, mean thrust and power coefficients are very close to those calculated in zero turbulence conditions, whereas fluctuations between 15% and 25% of the corresponding values in zero turbulence conditions are observed.