Effect of Flow-Induced Radial Load on Brush Seal/Rotor Contact Mechanics

Abstract

Brush seals comprised of special-alloy wire bristles are currently being used in lieu of traditional labyrinth seals for turbomachinery applications. This advancement in seal technology utilizes close-packed bristles that readily undergo lateral deformation arising from aerodynamic loads as well as loads imparted by the rotor surface. Thus, during operation, filament tips remain in contact with the rotor surface, which, in turn, inhibits leakage between successive stages of the turbine, and increases engine efficiency. However, contact forces generated at the interface of the rotor and fiber tips can lead to eventual bristle fatigue and wear of the seal/rotor system. Therefore, it is important that reliable modeling techniques be developed that can help identify complex relationships among brush seal design parameters, in-service loads, and contact forces that arise during the operation of turbomachinery. This paper is concerned with modeling and evaluating bristle deformation, bending stress, and bristle/rotor contact forces that are generated at the interface of the fiber and rotor surface due to radial fluid flow, and augments previous work reported by the author’s, which assessed filament tip forces that arise solely due to interference between the bristle/rotor. The current problem derives its importance from aerodynamic forces that are termed “blow-down,” that is, the inward radial flow of gas in close proximity to the face of the seal. Thus, bristle deformation, bristle tip reaction force, and bristle bending stress is computed on the basis of an in-plane, large-displacement mechanics analysis of a cantilever beam that is subjected to a uniform radial load. Solutions to the problem are obtained for which the filament tip is constrained to lie on the rotor surface, and includes the effect of Coulombic friction at the interface of the fiber tip and rotor. Contact forces are obtained for a range of brush seal design parameters including fiber lay angle, flexural rigidity, and length. In addition, the governing equation is cast in non-dimensional form, which extends the range of applicability of solutions to brush seals having a more general geometry and material composition.

The Effect of the Front Plate with Ribs on Brush Seal Flow Characteristics

“…By experimental methods Basu et al(1994) verified the fact that the contact force of the bristles with the rotor would increase after being exposed to the airflow, which causes the adverse effect of the rigidity of the bristles and reduces the service life of the brush seal. Stango et al,(1994)and Zhao et al(2003;2004) analyzed the contact force model of the bristle-rotor under different interferences in a two-dimensional plane, and studied the bristles as a hangover beam to analyze the influence of the bristles' design parameters, air force and radial interference on the contact force, and through experiments to verify the validity of the theoretical model. In order to simplify the interaction between the bristles, the porous medium model has become a broadly used mathematical model, and the bristle pack is regarded as a porous medium .…”

Theoretical and Experimental Investigation on Tip Forces and Temperature Distributions of the Brush Seal Coupled Aerodynamic Force

“…Demiroglu et al [5] applied linear and nonlinear beam theory approaches to derive tip forces caused by the assembly interference, and compared results with the experimental. Zhao and Stango [6] calculated the deformation and tip forces of a single bristle under uniformed aerodynamic forces utilizing large displacement mechanics analysis. They also discussed the influences of the bristle lay angle, flexural rigidity, and bristle length had on tip forces.…”

Effects of Front Plate Geometry on Brush Seal in Highly Swirling Environments of Gas Turbine

“…Basu et al [4] experimentally verified that the contact force between the bristles and rotor would increase after being exposed to the airflow, which causes the adverse bristle stiffness and reduces the service life of the brush seal. Stango et al [5] and Zhao et al [6,7] analyzed the contact force model between the bristle-rotor under different interferences in a two-dimensional plane and analyzed the effect of the bristles' geometric parameters on the contact force. Sun [8] investigated the bristle deflections and mechanical behavior based on the fluid-structure interaction model and conducted the experimental validation.…”