Measurement Of The Resonance Frequency Of The Aircraft Auxiliary Engine Load Compressor Impeller Blades

The resonant frequency of the impeller blades of APU load coInPressoris a target index necessary to be controlled in the process of themaintenance of iIllPeller. Through a mechanical analysis and test,this paper proves that, having been knocked to have an instantaneousactivation for a period of time, the soundscape generated by thefree oscillation with small--scale dase of the blades is mainly thebasic sound determined by the one--step inherent frequency, and theovertones determined by the higher--step inherent frequencies arerather feeble; moreoYer, the one--step resonant frequency of theblades closely approaches to their one--step inherent basic frequency.Therefore, the measurement of their one--step resonant frequency maybe converted to the measurement of their inherent frequency by usinga free attenuation curve procedure. That is to say, knocking theblades to generate measurable free attenuation sound signals andcoIIlParing the recorded time course with the time targets cancalculate the resonant frequency of the blades. Due to too muchshort sustained time duration of oscillation for the blades and toowide distribution of oscillation frequency over the audio frequencyrange, a procedure of variable gate frequency measurement has beenapplied to the design of frequency measuring instrument with amicro--controller unit (MCU) as its core. This procedure features ahigh precision and rapid speed. The measuring instrument for bladeresonant frequency mainly consists of a front end circuit, a signalcollecting circuit, and a coIIlPuting and displaying circuit. Thispaper provides a detailed hardware diagran, software flow chart anddesign process, expounds the operation and calibration of theinstrument, and analyses the measuring data in detail according todifferent conditions. Finally, this paper also suggests that theapplication of blade resonant frequency measuring instrument shouldbe combined with a mathematic method of two--grade fuzzy universalappraisal to form a novel and practical procedure to make acomprehensiye evaluation on the status of impel ler blades.