Abstract:In order to study of the unstable phenomena due to additional inertia forces during the runaway transients of hydropower units

the 3D simulation of the runaway transients in the whole passage of a bulb turbine was presented.The histories of pressure pulsation

rotating speed

torques

forces

and flow patterns were analyzed intensively.The results showed that the turbine blades endure asymmetrical alternating forces and the vortex rope structure in the draft tube is more complicate with breaking vortex rope because the gravitational water pressure gradient is apparent in this situation. In runaway process

the increasing rotational speed enhances significantly the flow impacts on blades

flow separations

and vortex rope intensity

causing severe pressure fluctuations.