Based on Reynolds-averaged continuity and Navier-Stokes equations, and moment equation of the rotational system in the accelerated rotational relative coordinate, the governing equations of the runner region are obtained. The runaway transient simulation of the Francis turbine based on HL220 is made with RNG k-ε turbulence model under 9 guide vane openings. The variation diagrams of volume discharge, moment, rotational speed, and efficiency with respect to time are gained. Through further analysis of simulation results the transient process curve as well as the flow pattern under 9 guide vane openings are obtained, and detailed analysis is focused on flow in the draft tube to obtain variation of pressure distribution on symmetry surface of the draft tube with respect to time and pressure fluctuation of all test points in the turbine. Comparison between simulation and experiment results shows that they both are in good agreement, and it demonstrates that variation of all the parameters of the hydraulic turbine can be forecast accurately during the transient process.

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