Abstract
Intentional mistuning is a common procedure to decrease the uncontrolled vibration amplification effects of the (unavoidable) random mistuning, and to reduce the sensitivity to it. The idea is to introduce an intentional mistuning pattern that is small, but much larger than the existing random mistuning. The frequency of adjacent blades is moved apart by the intentional mistuning, reducing the blade-to-blade coupling and, thus, the effect of the random mistuning. In order to clearly show the action mechanisms of intentional mistuning, we focus in this work in a quite simple configuration: forced response of a blade dominated modal family in a mistuned rotor with linear material damping. The problem is analysed using the asymptotic mistuning model methodology. A more reduced order model is derived that allows us to understand the relevant parameters behind the effect of intentional mistuning, and gives a simple expression for the estimation of its beneficial effect. The results from the reduced model are checked against detailed FEM simulations of two mistuned rotors.
Highlights
Mistuning refers to the unavoidable small differences between blades in a turbomachinery rotor
The application of the asymptotic mistuning model (AMM) methodology allows to understand the way of using intentional mistuning to reduce the vibration amplification and the sensitivity to the unavoidable underlying random mistuning, and the limitations of this strategy
The effective attenuation of the random mistuning effects using intentional mistuning is seen to depend on the relative value of three small effects: elastic coupling of the modal family, blade damping, and the random mistuning amplitude:
Summary
Mistuning refers to the unavoidable small differences between blades in a turbomachinery rotor. In the case of forced response excitation, a blade mass scatter of the order of 2–3% can lead to the localization of the vibration to a few blades which can show response amplifications of 200–300% [2]. These increased response levels result in a strong decrease of the fatigue life of the blades, and, have a considerable negative impact on the safety, operability and readiness of aircraft turboengines. The aim of this paper is to elucidate which are the conditions required for the intentional mistuning to reduce the negative effects of the existing small random mistuning on the forced response of a turbomachinery rotor. The AMM equations are used to study the effect of intentional mistuning, and the results and predictions obtained are verified against full FEM simulations of two mistuned rotors
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