Comparison of discharge characteristics of Pelton injector estimated by empirical relation, numerical simulation and experiment

Abstract It is difficult to define a general relationship for discharge characteristics of a Pelton injector due to high degree of variability in geometry of injector amongst different Pelton turbine designs. This study has been aimed to determine discharge characteristics of injector of Pelton rig at Waterpower Laboratory, NTNU. Three different approaches have been undertaken, viz. calculation based on empirical relations, numerical simulations, and experimental validation. For empirical calculation, the injector has been simplified into series of flow geometries with equivalent cross-sectional area and axial length for multiple stroke to constant aperture diameter ratio ( s/D 0 ). Discharge coefficient has been calculated for a constant pressure difference between inlet and atmospheric outlet for each case of s/D 0 , based on head loss estimated using empirical resistance coefficient ( ζ - values) available in engineering handbooks. Discharge has been determined through numerical simulations for same s/D 0 values. Results from numerical and empirical calculations are compared and correction factor (CF) has been determined. It is found that the CF is almost constant, at value of 0.85, for all values of s/D 0 . The discharge coefficient calculated by numerical simulation is around 0.02 lower than the values obtained by experimental observation.