Abstract
The modal identification of rotor blades in operating conditions is difficult for several reasons including the unavoidable transient effects that arise when resonances are crossed relatively fast. Algorithms to deal with this problem are available for the case of time-resolved signals (e.g. strain gauges), while for blade tip timing (BTT) data, the experience is much more limited, in particular as far as engines in operating conditions are concerned. This paper aims to contribute to the development and validation of system identification techniques applicable in transient conditions using BTT data. To this end, one method based on the fitting of the transient response and one method based on the fitting of the synchronous response are formalized, applied and compared to analyze the behavior of an operating engine in which both BTT and strain gauge measurements are available.