A one-dimensional model for predicting on/off design performance of impulse turbine stages was developed which accounts for the effects of secondary flows. The well known Craig and Cox loss model was implemented together with unconventional correlations for the estimation of secondary and volumetric effects (those related to leakage flows in labyrinth seals, shrouded rotors and open cavities, balance holes, as well as the volumetric effect due to rotor blockage). These effects were modeled according to off-line CFD simulations of turbine stages and, then, calibrated on experimental data of a number of real multistage impulse turbines. The result is a fast and reasonably accurate model, which can profitably be used for both design and analysis purposes.

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