3D CFD simulation of the runaway process of a Pelton turbine

During the runaway process of a Pelton turbine, the runner bears huge amounts of water pressure pulsations and centrifugal forces, which is different from the steady-state condition. In this work, a fine 3D CFD simulation of the runaway process of a Pelton turbine is performed. Both the macro-parameter changing patterns of rotational speed, torque and efficiency, and the micro-flow features of pressure pulsations and flow patterns are intensively studied and analyzed. It is found that the maximum runaway speed is 1.78 times of the rated speed, acceleration is the main feature in the early stage of runaway, and the jet fragment breaks away and strikes once again on the lip region and backside of the buckets in the middle and late stages. The multiple strikes make the frequency of pressure pulsations increase, and the cavitation occurs on the backside mold line. This successful 3D simulation shows that it is possible to simulate other transient processes of Pelton turbines and conduct fluid–structure interaction analysis of the runner.