Blade trailing edge position influencing pump as turbine (PAT) pressure field under part-load conditions

Abstract

Small hydropower is the most preferred clean energy technology, especially in remote areas away from national electrical grid reach. Within these plants, Pump as Turbines (PATs) suffer from a very small range of optimum operating conditions, leading to a chronic vulnerability to off-design conditions and associated flow instability, as well as the resultant pressure pulsations. PAT impeller design presents a great opportunity to alter the flow dynamics within PAT flow zone, probably leading to PAT performance improvement. In this respect, the present study seeks to investigate the effect of blade trailing edge hub position on pressure field characteristics within a centrifugal PAT. Using the k-ɛ turbulence model, unsteady numerical simulations were carried on a three centrifugal PAT with different blade trailing edge hub positions, namely 15 mm, 20 mm, and 25 mm. The results showed that for PAT pressure pulsations distribution, the Rotor-stator Interaction (RSI) constitutes the main influencing factor, where the Blade Passing Frequency and its harmonics were the dominant frequencies, for the three models. Moreover; different PAT models exhibited different pressure pulsation characteristics. The Rh20 model exhibited the highest level of pressure pulsation amplitudes, while the lowest level of pressure pulsation was recorded with Rh15 model.