Anti-Swirl Arrangements Prevent Rotor/Seal Instability

Abstract

Fluid involved in rotative motion (fluid “swirl”) within seals of high speed fluid handling machines is a recognized source of rotor instability. This type of instability leads to the limit cycle of rotor lateral precessional self-excited vibrations of a subsynchronous frequency. The anti-swirl concept is based on the injection of an additional flow to the seal, in the tangential direction, opposite to the direction of the shaft rotation. This flow causes a decrease of the shaft rotation-generated circumferential velocity of the fluid, and improves rotor/seal stability. In this paper the anti-swirl concept is outlined. The mathematical model of the rotor/seal system is analyzed. The analysis and experimental tests establish the physical basis of the anti-swirl concept. The fluid force model, based on the fluid circumferential average velocity of the flow, proves to be an adequate way to represent the seal fluid dynamic forces.

The Effect of Disk Location, Shaft Length and Imbalance on Fluid Induced Rotor Vibrations

“…The oil whirl behavior is observed to be at a constant vibration order of about 0.47 of the shaft revolution frequency and then the oil whip behavior is observed with a constant vibration frequency at around 3,850 cpm. Similar results can be found in the literature [8].…”

“…23). The results reflect those reported elsewhere [1,8]. Figure 24 shows the numerical solution for the natural frequencies of the system, in the form known as a Campbell diagram.…”

“…Factors affecting the oil instability and their application as possible solutions [8][9][10] have been described. Bearing factors such as clearance and anti-swirl were also studied.…”

Order reduction and nonlinear behaviors of a continuous rotor system

“…The fluid film radial stiffness, damping and inertia effects are described by nonlinear functions of the rotor eccentricity ratio inside the bearing and seal. The model has been used to analyze anti-swirl to correctly and effectively prevent rotor/seal instability [7]. Adopting the Muszynska model, Ding et al [8] investigated the Hopf bifurcation of a rotor/seal system.…”

Response Characteristics of Looseness‐Rubbing Coupling Fault in Rotor‐Sliding Bearing System

“…In order to simulate the nonlinearity of the sliding bearing, some nonlinear oil film force models have been proposed, such as Capone G [1,2]. The Muszynska model [3][4][5] was introduced as a simple model of nonlinear fluid dynamic forces generated in bearings as well as in seals based on the results of a series of experiments. A parameter called the fluid average circumferential velocity ratio is used to describe the characteristic of the fluid motion as a whole.…”