Reduced Order Models for Blade-to-Blade Damping Variability in Mistuned Blisks

Abstract

A novel reduced order modeling methodology to capture blade-to-blade variability in damping in blisks is presented. This new approach generalizes the concept of component mode mis-tuning (CMM) which was developed to capture stiffness and mass mistuning (and did not include variability in damping amongst the blades). This work focuses on modeling large variability in damping. Such variability is significant in many applications, and particularly important for modeling damping coatings. The damping in each of the blades is assumed to be structural at the blade level. However, variability in the damping coefficients of the blades means that the damping is not structural at the system (entire blisk) level. Similar to the CMM based studies, structural damping is used to capture the damping effects due to the mechanical energy dissipation caused by internal friction within the blade material. The steady state harmonic responses of the blades are obtained using the novel reduced order modeling methodology, and are validated by comparison with simulation results obtained using a full order model in ANSYS. The effects of damping mistuning are studied statistically through Monte-Carlo simulations. For this purpose, the blisk model is subjected to multiple travelling wave excitations. The uncertainty in the various mechanisms responsible for dissipation of energy and the uncontrollability of these dissipation mechanisms makes it difficult to assign a reliable value for the loss factor of each blade. Hence large variations (up to ±80%) in the structural damping coefficients of the blades are simulated.

Hybrid modal damping identification for bladed disks and blisks

“…As mistuning may adversely affect some modes more than others, it is important to increase as much as possible the damping of certain/desired modes. Joshi and Epureanu (2011) showed that an arbitrary damping coating does not always optimally decrease the maximum response of the desired modes as one might expect. Therefore, to assess the effects of a coating, damping must be identified before and after the coating is applied.…”