CFD and comparisons for a pump as turbine: Mesh reliability and performance concerns

The need for saving energy in water supply systems has become one of the main concerns of system managers and it will become more important in a near future. New strategies must be developed and implemented in the major energy consumption systems like those for water supply. In drinking pipe systems the use of Pressure Reducing Valves (PRV) as a dissipative device is the common way to uniform the pressure control through a localised head loss. The use of micro-turbines or pumps operating as turbines seem to be an alternative technical and environmental available solution to either control the pressure as well as to produce energy. Pumps as turbines (PAT) could be a convenient choice, but a deep study of the machine in different operating conditions is necessary in order to prevent the water system from ruptures. This paper shows that semi-empirical parametrical models do not generally predict with precision the behaviour of a pump operating as a turbine, while CFD analysis could be a reliable tool to better understand the interaction between the hydromechanical equipment and the flow behaviour. Nevertheless the CFD calculation difficulty is generally very high and the minimum complexity of the CFD calculation mesh has been investigated, in order to perform faster and reliable simulations. Thus CFD calculations have been carried out to predict the turbine behaviour under different flow conditions and the performance curves have been obtained. Some calculations in unsteady state flow regimes have been led to investigate the response of the machine to a sudden discharge changing, as a preliminary study of the behaviour of a turbomachine installed in a water distribution system under water hammer situations. Copyright © 2011 International Energy and Environment Foundation - All rights reserved.