Aerodynamic-Rotordynamic Interaction in Axial Compression Systems—Part II: Impact of Interaction on Overall System Stability

Abstract

This paper presents an integrated treatment of the dynamic coupling between the flow field (aerodynamics) and rotor structural vibration (rotordynamics) in axial compression systems. This work is motivated by documented observations of tip clearance effects on axial compressor flow field stability, the destabilizing effect of fluid-induced aerodynamic forces on rotordynamics, and their potential interaction. This investigation is aimed at identifying the main nondimensional design parameters governing this interaction, and assessing its impact on overall stability of the coupled system. The model developed in this work employs a reduced-order Moore-Greitzer model for the flow field, and a Jeffcott-type model for the rotordynamics. The coupling between the fluid and structural dynamics is captured by incorporating a compressor pressure rise sensitivity to tip clearance, together with a momentum based model for the aerodynamic forces on the rotor (presented in Part I of this paper). The resulting dynamic model suggests that the interaction is largely governed by two nondimensional parameters: the sensitivity of the compressor to tip clearance and the ratio of fluid mass to rotor mass. The aerodynamic-rotordynamic coupling is shown to generally have an adverse effect on system stability. For a supercritical rotor and a typical value of the coupling parameter, the stability margin to the left of the design point is shown to decrease by about 5% in flow coefficient (from 20% for the uncoupled case). Doubling the value of the coupling parameter not only produces a reduction of about 8% in the stability margin at low flow coefficients, but also gives rise to a rotordynamic instability at flow coefficients 7% higher than the design point.

Modified oil film force model for investigating motion characteristics of rotor-bearing system

“…Many studies and numerical calculations have been carried out to analyze the dynamic response of the rotor system under the effect of oil film force. A symmetric rotor system (Al-Nahwi et al, 2003) is investigated, where the Muszynska nonlinear model was used to describe the fluid force and the Hopf bifurcation of the system was analyzed. The principle and interaction of steam excitation is investigated on a Jeffcott rotor system combining the Moore-Greitzer Fow Eeld model (Hua et al, 2005).…”

Research into the dynamic coefficient of the rotor-seal system for teeth-on-stator and teeth-on-rotor based on an improved nonlinear seal force model

“…Ding et al (2000) investigated a symmetric rotor/seal system, where a Muszynska nonlinear model was used to describe the steam excitation force and the Hopf bifurcation of the system was analyzed. Al-Nahwi et al (2003) investigated the principle and interaction of steam excitation on a Jeffcott rotor system combining the Moore-Greitzer Fow Eeld model. Li et al (2003) employed Muszynska's model to describe steam excitation force in labyrinth seals, calculated periodic solutions of a Jeffcott rotor system based on shooting procedure and analyzed its stability (Bently and Muszynska, 1988;Li, 2003).…”

Modeling a two-span rotor system based on the Hamilton principle and rotor dynamic behavior analysis

“…The Muszynska model highlights the seal force nonlinear characteristics with clear physical meaning (Muszynska and Bently, 1990). Al-Nahwi et al (2003) analyzed the principle and interaction of steam excitation on the Jeffcott rotor system combining it with the Moore-Greitzer flow field model. Luo et al (2007) built a periodical time-variable high-dimensional dynamic rotor system based on the rotor's finite element model and investigated the stability of the system.…”