Aero-elastic excitation can result in excessive blade vibration, which can cause blades to fail in high cycle fatigue (HCF). A severe aero-elastic failure can result in a complete blade separation and loss of thrust and loss of a blade can mean the loss of an aircraft. The primary aeromechanical design concerns are blade flutter and forced vibration that need to be quantified at the early part of engine tests. This paper details the experimental investigation carried out on a transonic shroudless low aspect ratio fan bladed disk that experienced subsonic/transonic stall flutter and forced vibration excitation. Experiments are performed on a full scale engine using tip timing sensors flush mounted on the fan casing to characterize the vibratory responses during flutter and forced vibration conditions during engine operation. Numerical simulations are performed using computational fluid dynamic (CFD) analysis. Blade natural frequencies and mode shapes are obtained from finite element (FE) modal analysis. The experimental data captured from engine tests are used to validate the predicted results.© 2013 ASME

Rotor blade vibration in turbomachinery has been a major cause of failure due to HCF, often resulting in catastrophic damage. The primary aeromechanical design concerns are blade flutter and forced vibration that need to be quantified. The severity of blade vibratory response is almost impossible to predict using theoretical tools as it depends on the strength of excitation. Hence in order to evaluate the HCF characteristics of rotating blades, aero industry depends on measurements for actual vibratory response during engine tests. Various methods are used for measurement of rotor blade vibration. Conventionally strain gauges are extensively used for characterizing vibratory signatures of rotating blades. However, the strain gauges have their own limitations posed by operating temperatures and high-end technology is required to transmit signal from rotating components. Hence only a few blades in a rotor can be instrumented resulting in limited data capture. This paper presents a non-contact type of measurement technique using blade tip timing to capture vibratory signatures of all the blades of the rotor stage. This method is used to characterize monitor rotor blade vibrations of Low-Pressure Compressor and Low-Pressure Turbine of a developmental gas turbine engine. It has provided valuable data with respect to incipient damages, preventing catastrophic failure.

Flutter and Forced Vibration Characteristics of a Turbo Fan Bladed Disk Rotor

Citations

Rotor Blade Vibration Measurement on Aero Gas Turbine Engines

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