Unsteady Vibration of a Gas Turbine Compressor Blade at Subsonic Near-Stall Conditions

Cascade wind tunnel tests were conducted to clarify unsteady blade vibration characteristics near stall conditions. An oscillating strain and pressure on a blade surface were measured. An aerodynamic damping ratio was also measured using the sweep excitation method and the operational modal analysis. Moreover, an unsteady blade vibration response and aerodynamic damping ratios were calculated using a three-dimensional computational fluid dynamics and a three-dimensional structural finite element method.As a result of the experiments, the natural frequency component oscillated by the broadband frequency component of the fluid force was dominant in the stress, while the discrete low frequency components appeared in the pressure. The amplitudes of the stress and pressure increased when the Mach number or the incidence increased. As a result of the calculations, the discrete low frequency components appeared in the pressure, and those components and the natural frequency components appeared in the stress. The experimental and calculation results of the stress amplitude were generally in agreement.The measured damping ratios increased when the Mach number increased. The dispersion of the measured damping ratio using the operational modal analysis was small. The calculated damping ratio was 1.3–1.8 times larger than the measured result.Copyright © 2013 by ASME