Numerical analysis of the compromise between power output and fish-friendliness in a vortex power plant

Abstract The characteristics of a vortex power plant integrated in a weir have been investigated using computational fluid dynamics, with a special focus on all flow properties relevant to fish migration and energy conversion. The numerical model relies on a Reynolds-averaged, unsteady description using the volume-of-fluid method to describe the free surface. Several monitors are implemented, quantifying, in particular, the distribution of water velocities within the plant, and the probability of impact between drifting objects and turbine blades. Parameters, such as volume flow rate, turbine clearance, turbine speed and number of turbine blades have been varied. The systematic observation of the distribution of velocities and power density help assess the ecological impact of those modifications. It is found that a moderate increase of the turbine clearance and a reduction of the number of blades provide an attractive compromise between power output and opportunity for easy migration. Finally, it is predicted that the hazard associated with a fish hitting turbine blades can be greatly reduced by a careful adaptation of the turbine rotation velocity. Those developments are a first step towards a systematic numerical assessment of the fish-friendliness of machines operating under stringent ecological regulations.