Blade Vibrations of a High Speed Compressor Blisk-Rotor: Numerical Resonance Tuning and Optical Measurements

Abstract

A major challenge during the design process of a modern low aspect ratio high speed axial compressor is to find rotor blade geometries that meet both, aerodynamic and mechanical requirements. This paper deals with the mechanical design of a transonic compressor blade. In order to meet the mechanical requirements in a short development time, new methods were used: A numerical optimization tool and an optical blade vibration measurement method: The numerical resonance tuning took advantage of a semi-automatic optimization technique, based on a Finite Element vibration anlysis tool. The intention was to find a geometry which has no critical resonances (with fundamental engine orders) within the operation range. To verify the calculated blade natural frequencies and eigen-values standard shaker tests using a laser holography system were carried out. Blades under g-load in the running compressor were investigated with an in-house developed vibration measurement system. This system is able to measure frequencies and amplitudes of the rotor blade vibrations without blade instrumentation but small optical probes, mounted in the compressor casing. The measured resonance points are in good agreement with the predictions. All amplitudes are far below the blade fatigue limits.