Influence of secondary flow rate on dynamic stresses in turbine rotor blades

A drawback to previous methods of estimating the dynamic stresses during turbine rotor blade vibration, which are based on studies of the degree of flow velocity nonuniformity in the gap between blading rings, is the lack of data on the extent of flow nonuniformity parameters in the end regions. The dynamic stresses from bending and torsional oscillations of turbine rotor blades were determined at the fundamental frequency of the resonant bending oscillations. The qualitative picture of the impact of secondary flow rates in the end regions on the dynamic stresses is discussed. The experimental configuration for the strain gauge measurements is illustrated. The secondary flows are controlled by means of additional vanes which are inserted between the rotor blades to reduce the level of stress both at the tip and root of the blades. The dimensions of added vane for optimal stress reduction are given. The measured dynamic stresses at the blade roots are shown to be the total bending and torsional oscillation stresses of the rotor blades.