Novel Frame Model for Mistuning Analysis of Bladed Disk Systems

Jie Yuan,Giuliano Allegri,Branislav Titurus,Ramesh Rajasekaran,Sophoclis Patsias,Fabrizio Scarpa

doi:10.1115/1.4036110

Abstract

The work investigates the application of a novel frame model to reduce computational cost of the mistuning analysis of bladed disk systems. A full-scale finite element (FE) model of the bladed disk is considered as benchmark. The frame configuration for a single blade is identified through structural identification via an optimization process. The individual blades are then assembled by three-dimensional (3D) springs, whose parameters are determined by means of a calibration process. The dynamics of the novel beam frame assembly is also compared to those obtained from three state-of-the-art FE-based reduced order models (ROMs), namely: a lumped parameter approach, a Timoshenko beam assembly, and component mode synthesis (CMS)-based techniques with free and fixed interfaces. The development of these classical ROMs to represent the bladed disk is also addressed in detail. A methodology to perform the mistuning analysis is then proposed and implemented. A comparison of the modal properties and forced response dynamics between the aforementioned ROMs and the full-scale FE model is presented. The case study considered in this paper demonstrates that the beam frame assembly can predict the variations of the blade amplitude factors, and the results are in agreement with full-scale FE model. The CMS-based ROMs underestimate the maximum amplitude factor, while the results obtained from beam frame assembly are generally conservative. The beam frame assembly is four times more computationally efficient than the CMS fixed-interface approach. This study proves that the beam frame assembly can efficiently predict the mistuning behavior of bladed disks when low-order modes are of interest.

Highlights

A bladed disk typically consists in a set of disk-blade sectors that are designed to be identical
The mistuning problem is still considered a challenge from a design perspective, because of the high computational costs associated with the dynamic analysis, even when using state-of-the-art reduced order models (ROMs)
This work provided a comparative study to assess the computational efficiency of a novel frame assembly for the mistuning analysis of bladed disc systems

Summary

Introduction

A bladed disk typically consists in a set of disk-blade sectors that are designed to be identical. The material and geometry uncertainties are further exacerbated by the operational wear and tear, as well as the non-conformal assembly of the blades [1]. These uncertainties will lead to the deviation of the blade natural frequencies (NFs) from their nominal design value; this phenomenon is commonly denoted as mistuning. One of the key aspects of mistuning analysis is how to quantify efficiently the effect of all the uncertainties mentioned above on the maximum dynamic response of bladed discs [6]. The mistuning problem is still considered a challenge from a design perspective, because of the high computational costs associated with the dynamic analysis, even when using state-of-the-art reduced order models (ROMs). This is commonly based on probabilistic methods such as Monte Carlo simulations (MCS), which usually requires running thousands of simulation runs [7]

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Conclusion