Vibrations and Stability of Turbine Blades at Stall

A method is given for analyzing the vibrations of turbine blades subjected to flows at high negative incidence angles. The conditions for the existence of self-excited vibrations and the stability of these vibrations are derived for free-standing or grouped blades which are of tapered and twisted form. The technique given extends the analysis of Sisto [1] to the case in which any mode of vibration may be considered and in which the aerodynamic forces and moments taken on a quasi-steady basis are functions of Mach number as well as instantaneous angle of attack. Results are given for a group of four lashed blades and some experimentally observed behavior is reported.