Leakage loss estimation and parametric study on the effect of twist in rotor shape for harnessing Pico hydropower

Abstract

Renewable energy will play an important role in achieving the energy stability and reducing the dependence on fossil fuels. Hydropower is one of the cheapest and reliable sources of renewable energy. The potential of micro and Pico hydro power is not yet fully explored. They can prove to be decisive in generating clean energy from conventional and un-conventional resources and making the systems energy efficient for sustainable development. The present work illustrates the Pico hydro power generation potential of a new class of hydraulic turbine known as positive displacement turbine (PDT). In addition, a parametric study was done to find the effect of twist in rotor geometry on the flow pulsations, leakage losses and the overall performance of the PDT using computational fluid dynamics (CFD). The performance of positive displacement type of hydraulic machines is very sensitive to leakage losses through clearances, which are very difficult to estimate. A mechanism was developed to qualitatively and quantitatively analyze and calculate the leakage losses. From the analysis, it was inferred that twisting the rotor geometry significantly reduced the flow pulsations; however this increased leakage flow from the rotor-rotor clearance. This caused a slight reduction in the performance of PDT. The optimum twist angle was found to be 45°. The relative increase in the average leakage flowrate ratio for various twisted rotor designs as compared to the base non-twisted rotor design was approximately in the range of 2–18%. The relative decrease in the theoretical hydraulic and volumetric efficiencies for various twisted rotor designs as compared to the base design was approximately in the range of 0.1–3%.