Reduced Order Modeling For Blisks And Its Application On Hard-Coating Blisks

As an important component of modern high-performance turbines,blisks have the advantages of light weight,simple structure and high reliability.Since blisks have no connection structure between blades and disks,its structural damping is lower than that of the conventional bladed disks,and some conventional damping structures are also difficult to apply thereon.In addition,due to the influence of mistuning,the vibration level of the structure is greatly increased.Therefore,reasonable damping measures should be taken to prevent the blisk from causing damage and failure due to excessive vibration.As a new damping method,hardcoat damping has excellent damping performance and good resistance to high temperature and corrosion,so it can be applied to blisks.In order to better apply the hard coating on blisks,it is necessary to study and develop the finite element reduction modeling method for the mistuned blisks to effectively estimate the vibration level of the hard-coating blisks.The research content of this paper includes:(1)Two calculation principles of the cyclic-symmetry algorithm were given systematically,and the process of obtaining the frequency and mode shape of the entire tuned blisk using the single-sector model was given in detail.In addition,the finite element model of the composite structure of the hard-coating blisk was established,and the correctness of the modeling was verified by experiments.Finally,the vibration characteristics of tuned blisks before and after coating treatment were analyzed,and the damping effect of the hard coating on the tuned blisk was verified.(2)The reduced-order models of mistuned blisks before and after coating treatment were established according to the Subset of Nominal System Modes(SNM).Next,considering the distribution range of the actual random mistuning,the random mistuning was simulated by using the truncated normal distribution.Then,using the reduced-order model as the calculation tool,the statistical characteristics of the amplitude amplification factor of mistuned blisks before and after coating treatment was studied by Monte Carlo simulation.Finally,the damping characteristics of NiCrAlCoY+YSZ coating on mistuned blisks were summarized.(3)Intentional mistuning and damping were achieved by applying large-damping hard coatings of different thicknesses on different blades.Firstly,characteristics of the classical coating patterns based on NiCrAlCoY+YSZ material were studied,and the mechanism and effect of damping mistuning were explained,thus improving the intentional coating patterns.Finally,vibration-suppressing characteristics of the improved intentional mistuning coating patterns were studied.The results showed that the improved intentional mistuning coating patterns can greatly reduce the vibration level of mistuned blisks and the sensitivity to mistuning.(4)Based on a special hybrid interface method,a novel reduced-order model for blisks with both large and small mistuning was proposed.First,taking the blisk with a geometric mistuning sector as the research object and considering random mistuning level small,the blisk was divided into a damaged component and a remaining component.The displacement of the remaining component was represented as a linear combination of cyclic modes only containing the DOFs(degree of freedom)of the remaining component,and the displacement of the damaged component was obtained by the Craig-Bampton fixed interface method.Thus a basis matrix was obtained through the process of modal synthesis.Then,the low-order modes of the blisk can be represented as the linear combination of the columns of the basis matrix,thereby realizing the reduction of the system by using the basis matrix.When the random mistuning level became medium or higher,it was proposed to use the subspace iteration method to update the basis matrix.Next,taking a blisk with large mistuning and random mistuning as a numerical example,natural frequencies,mode shapes and forced response calculated by the reduced-order model were compared with the results calculated by ANSYS software to verify the correctness of the reduced-order model.Finally,the future application of this method on hard-coating blisks was discussed.Hard coatings have a broad application for vibration suppression of blisks.The cyclic symmetry,reduced order modeling,intentional mistuning modeling,and large mistuning modeling methods discussed in this paper can provide effective tools to model different hardcoating blisks and capture their dynamics.