Aerodynamic performance improvements for a Savonius turbine above a forward-facing step via inclined solar panel : a computational study

Abstract

The transformation of urban energy structure is an urgent problem to be solved in sustainable construction. To fully exploit and utilise renewable energy, this study proposes a novel wind–solar energy hybrid harvesting system that combines an inclined solar panel and a Savonius wind turbine installed on a building roof. The effects of the tilt angle of the solar panels and tip speed ratios (TSRs) on the aerodynamic performance of the turbine were investigated using high-fidelity large-eddy simulations (LES) at a Reynolds number of Re = 4.45 × 105. Five tilt angles in the range of 30°–60° were tested, and the range of TSR was 0.2–1.6. For comparison, two other installation cases were also studied, including the case of a Savonius turbine alone and the case of a single Savonius turbine placed at a fixed height position on a forward-facing step. The results showed that the power coefficient of the Savonius turbine increased and then decreased with tilt angle or TSR. When TSR = 1, the power coefficient in the system reached a maximum value of Cpmax = 0.638 at a tilt angle of 45°, 254.4% and 11.7% higher than those of the other two installation cases, respectively. The flow-field comparison results reveal why the proposed system can improve the energy harvesting efficiency. The presence of a solar panel with a suitable tilt angle increases the velocity and volume of the airflow hitting the advancing blade, creating a greater pressure difference around the blades that is caused mainly by the decrease in the low pressure on the concave surface of the advancing blade. Thus, the net torque applied to the turbine blades increases, which is conducive to driving turbine rotation. The proposed system is beneficial for improving the aerodynamic performance of Savonius turbines and the utilisation of renewable energy in urban areas.