Abstract
The present paper is focused on the post processing of the data coming from the Blade Tip-Timing (BTT) sensors in the case where two very close peaks are present in the frequency response of the vibrating system. This type of dynamic response with two very close peaks can occur quite often in bladed disks. It is related to the fact that the bladed disk is not perfectly cyclic symmetric and the so called “mistuning” is present. A method based on the fitting of the BTT sensors data by means of a 2 degrees of freedom (2DOF) dynamic model is proposed. Nonlinear least square optimization technique is employed for identification of the vibration characteristics. A numerical test case based on a lump parameter model of a bladed disk assembly is used to simulate different response curves and the corresponding sensors signals. The Frequency Response Function (FRF) constructed at the resonance region is compared with the traditional Sine fitting results, the resonance frequencies and damping values estimated by the fitting procedure are also reported. Accurate predictions are achieved and the results demonstrate the considerable capacity of the 2DOF method to be used as a standalone or as a complement to the standard Sine fitting method.
Highlights
Turbomachinery blades can reach critical vibration amplitude during operating conditions.Undesirable vibrations occur when the blade passes through a resonance
The paper is focused on the post processing procedure of the Blade Tip-Timing (BTT) sensors data in the case where two very close resonance frequencies are present in the dynamic response of the rotating system
Having two close resonance peaks is the typical case of the dynamic response of a bladed disk in presence of mistuning, due for example to an asymmetry of the distribution of the mass in the disk
Summary
Turbomachinery blades can reach critical vibration amplitude during operating conditions. Undesirable vibrations occur when the blade passes through a resonance. Blades vibrations can be excessively increased with the risk of incurring a High Cycle Fatigue failure. Vibration measurements of rotating blades are traditionally performed by means of strain gauge technology [2]. This method has been developed over time and successfully employed for an extensive range of engineering applications. It is considered as a well-established technology with the most accurate and reliable results.
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