EFFECT OF ENLARGED FREE JET ON ENERGY CONVERSION IN PELTON TURBINE

In Pelton turbines, when the water jet emerges in the air, its velocity decreases downstream and its diameter increases to meet the continuity. In this paper, a physical parameter, the enlarging rate of jet diameter kDj was introduced and measured experimentally. The measurement of enlarging rate was carried out in three model turbines with different distributing Y-branch and nozzle configurations under various operating conditions. The effect of jet enlarging rate on the unsteady water sheet flow in the rotating buckets has not been investigated so far. This paper also presents the comparative numerical analysis of the flow in buckets at different enlarging rates of jet. It is shown that the effect of jet enlargement is so large that the flow pattern in the bucket is drastically changed by the latter half of the frames. The jet with large enlarging rate also introduces worse energy behavior to the hydraulic performance of the Pelton turbine. Besides, the phenomenon of jet interference was also discussed by using the results of numerical simulation for one jet. It indicates that the jet with large enlarging rate takes more risk that jet interference may damage the performance of multi-nozzle Pelton turbine.