Hydraulic performance evaluation of a micro-turbine with counter rotating runners by experimental investigation and numerical simulation

The development of energy recovery systems on existing water utility networks is a new challenge for increasing the sustainability of electricity generation mix. The concept of the new micro-turbine with counter rotating runners braces this goal by allowing the recovery of the energy which is spoiled in pressure reducing valves in many water supply networks. The hydraulic performances of the micro-turbine are evaluated through an analysis on the angular momentum balance applied to the investigated cross-sections of the machine. For this analysis, an experimental campaign involving 2D Laser Doppler Velocimetry (LDV) is performed to measure the velocity field of the flow at the inlet and outlet sections of the machine. Since the optical access to perform LDV measurements is blocked close to the hub of the runners, a further analysis on the mass balance and numerical simulations are performed to complete the velocity profiles and to evaluate the machine performance. The combination of numerical and experimental methods grants a full study on the operating condition of the micro-turbine and strengthens the results achieved. The results back up the best operating condition of the machine for different discharges and support further improvements of the runner blades shape.