Runaway numerical investigation of a six-nozzle model Pelton turbine- A case with emphasis on transient flow and energy transportation analysis

During Pelton turbine runaway, rotational speed rises rapidly and the runner flow remains highly turbulent, reducing unit stability and inducing strong hydraulic vibrations that shorten component life. This study applies the finite volume method to simulate transient flow in a six-nozzle Pelton model from rated to maximum speed. Comparison with model tests shows runaway speed errors within 5%, ensuring result reliability. The findings reveal that during runaway, as rotational speed increases, torque decreases, while the overflow velocity at the outlet edge rises from below 1 m/s to above 35 m/s, indicating intensified turbulent fluctuations in the runner region that significantly hinder the incoming jet. The amplitude of runner hydraulic thrust fluctuations rises, with the axial thrust pulsation at a 24 mm opening nearly doubling that at a 12 mm opening, increasing the risk of accidental impacts between adjacent components. Energy dissipation in the runner is primarily driven by Reynolds stress work and turbulent kinetic energy production, accounting for over 80% of total dissipation, As speed increases, pressure-side high-energy clusters, which is regions of rapid energy transfer and dissipation, move forward, while intensified suction-side splashing enlarges the high-energy region.