STABILITY OF BLADE-CASING INTERFERENCE IN TURBOMACHINERY AND THE DESIGN ALTERNATIVES ON DAMPING CHARACTERISTICS

Bladed disks in turbomachinery are commonly designed to operate within a very small clearance from the stationary shroud (casing). For variety of reasons, however, they interfere with each other during routine operation which results in undesirable vibrations. The novel idea in this paper originates from the claim that this dynamics is inherently akin to internal machining operation which uses compliant cutters (blades) with relatively rigid workpiece (casing). It is known that machining processes suffer from a phenomenon called chatter, which has been studied over decades to a considerable extend. We propose a new perspective to investigate the stability of blade-casing contact vibrations by a modeling approach borrowed from chatter literature. The mathematical model arises with a signature time-delayed dynamics for which we utilize a recent analytical tool called the Cluster Treatment of Characteristic Roots (CTCR). We present an exhaustive stability analysis and study the effects of altering damping characteristics in the casing structure.