An Investigation of Tip Force Characteristics of Brush Seals

Abstract

Thanks to their compliant nature and superior leakage performance over conventional labyrinth seals, brush seals found increasing use in turbomachinery. Utilizing high temperature super-alloy fibers and their compliance capability these seals maintain contact with the rotor for a wide range of operating conditions leaving minimal passage for parasitic leakage flow. Consequently, the contact force/pressure generated at seal rotor interface is of importance for sustained seal performance and longevity of its service life. Although some analytical and numerical models have been developed to estimate bristle tip pressures, they simply rely on linear beam equation calculations and other such assumptions for loading cases. In this paper, previously available analytical and/or numerical models for bristle tip force/pressure have been modified and enhanced. The nonlinear cantilever beam equation has been solved and results are compared to a linear cantilever beam equation solution to establish application boundaries for both methods. The results are also compared to experimental data. With the support of testing, an empirical model has been developed for tip forces under operating conditions.

Numerical Investigations on the Heat Transfer Behavior of Brush Seals Using Combined Computational Fluid Dynamics and Finite Element Method

“…As expected, the bristle-rotor normal contact force and frictional force almost linearly increase as pressure differential across the seal increases. These linear relationships are agreed with the experimental measurements of Demiroglu et al [16] and Crudgington et al [28]. The increasing pressure differential enhances the aerodynamic force on the bristles.…”

“…Demiroglu et al [16] modified analytical solution for bristle tip force based on linear beam theory with the help of extensive testing and previous numerical work. Their analytical solution with consideration of friction between bristles and bristles to backing plate gave reasonably good estimation without a need for cumbersome detailed numerical modeling or testing.…”

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

“…Generally, the frictional heat Q is related to the frictional coefficient ß, the normal reaction force Fb and the rotor surface speed v. Literature in Ref. [5] proposed a frictional heat equation…”

“…The study of tip forces is very difficult and involves many integrated issues, such as fluid flow, solid-fiuid interactions, contact mechanics and tribology. 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.…”

Influence of Friction on the Blow-Down Behavior of an Aramid Fiber Brush Seal

“…A close-up view of an aramid fiber brush seal is shown in Figure 1. Metallic brush seal design has been discussed at length in the literature [3][4][5][6][7][8][9][10][11][12][13][14][15][16], including investigations into bristle pack stiffness and heat generation at the bristle pack -rotor interface. Recent investigations have been published on similar design philosophies for aramid fiber brush seals, particularly aimed at compressor sealing applications in the Oil and Gas market.…”