Author(s): Leandro Duarte; Nicolas Maguin; Guilhem Dellinger; Nicolas Dellinger; Thomas Keraudren; Jose Vazquez
Keywords: Spherical turbine; Vertical-axis turbine; Pipe flow; Small hydropower; Numerical modelling
Abstract: The purpose of this work has been to study a novel concept of spherical turbine for power extraction in pipe flow. It consists of a two-bladed vertical-axis turbine with NACA0015 blades. The originality of this novel design lies in its ability to drastically minimize the pressure losses induced in the flow by the turbine under stationary conditions. A simplified 2D numerical model has been implemented in OpenFOAM. Following a sensitivity analysis, a baseline model has been set with about 90,000 cells and y+<1 over the blades. An arbitrary mesh interface (AMI) ensures a constant rotational speed of the turbine, with 3,000 time steps per revolution. Turbulence is modelled in a RANS approach by the one-equation model of Spalart-Allmaras. The numerical model has then been employed for investigating different variations of the turbine design. The influence of two of the main design parameters – namely solidity and tip-speed ratio – on the energy harvesting performance of the turbine has been characterized. The numerical results suggest that this novel turbine could harvest up to more than five times the hydrokinetic energy of the incoming flow. Indeed, a 3D numerical investigation should be carried out to account for the curvature of the blades and flow deflection by the spherical turbine. Nevertheless, the present study provides a very encouraging first-order evaluation of the performance of this novel concept of turbine for power extraction in pipe flow.