Analysis of fixed turbine operating conditions with and without a shock capture scheme

A better simulation of tidal-stream energy capture and its effects on local hydrodynamics, at the regional scale, should incorporate the Turbine Operating Conditions (TOC). An approximation to a simple turbine which does not adjust the turbine blade pitch control system is investigated numerically with the momentum sink-TOC method. It is based on the linear momentum actuator disc in open channel flows theory (LMADOCH) and momentum sink method. The momentum sink-TOC computes the energy capture considering a device with constant blockage ratio, B, and wake-induction factor, α₄. The increasing drag imposed by the turbines on the tidal-stream was investigated by evaluating a set of α₄ and using a fence and a partial-fence configuration. To determine the relevance of using a shock-capturing scheme to model the spatial gradients produced in the tidal-stream by power extraction and turbine drag increase two hydraulic models were used. The first one uses a conventional strategy to model Gradually Varying flow (GVF) and the second incorporates a shock-capturing scheme to model Rapidly Varying flow (RVF). An RVF model approximates more accurately the spatial perturbations occurring in the vicinity of the turbine array produced by power extraction and drag increase. Particularly satisfactory results were obtained for a partial-fence. These results suggest that modelling of a turbine with fixed operating conditions can better approximated with an RVF scheme.