Abstract
Jet interference brings serious deterioration of efficiency in multinozzle Pelton turbines especially in the operating region of higher unit speed and higher unit discharge. Since the jet interference is intensified by the scale effect of the specific hydraulic energy for a turbine, it is difficult to predict the jet interference of a prototype from is low-head model test results. An alternative approach for predicting prototype interference is therefore urgently required. In our 1st report, a newly proposed intensity for the jet interference based on the relative jet paths reveals a good correlation with the efficiency deterioration due to the jet interference. In the present report, the scale effect of specific energy on the jet interference intensity is investigated. The velocity coefficient of a free jet is reduced with increasing specific hydraulic energy of the turbine, because the entrainment of water droplets in the turbine housing into the free jet increases with the increase of jet flow rate, or of specific energy. Using the relative jet paths considering the decay of jet velocity, the predicted intensity of jet interference shows a good correlation with the increased deterioration of efficiency due to the scale effect of specific energy.
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