Runaway characteristics of a prototype bulb turbine considering upper and lower reservoirs based on lattice Boltzmann method

Abstract

As a hydraulic machinery commonly applied for developing tidal energy, a bulb turbine is inevitable to experience the runaway process during operation. The performance parameters and internal flow of a bulb turbine evolves sharply during the runaway process, seriously affecting the stability of the unit. The runaway process in a bulb turbine is more sensitive to the gravity and the free level of upper and lower reservoirs due to the low working head. In this work, the runaway process in a prototype bulb turbine with upper and lower reservoirs is investigated by using the lattice Boltzmann method, which can avoid the problem of difficult grid reconstruction. Experiments are conducted to obtain the unit runaway speed of the bulb turbine. Results show that the unit runaway speed predicted by numerical simulation agrees well with that measured by experiments. The runaway characteristics of the bulb turbine with and without reservoirs are compared. During the runaway process, the variation of parameters of the bulb turbine mainly undergoes two stages, severe and stably periodic fluctuation period. The evolution of flow behaviour with time is analysed in detail, which can improve the understanding of flow characteristics in the bulb turbine during the runaway process.