Modeling, analysis and design considerations for brush seals used in turbomachinery

Haifang Zhao, Marquette University


Brush seals have proven to be an attractive alternative to labyrinth seals for turbomachinery applications. This advanced seal technology utilizes both the high temperature capability of special-alloy wire and flexure adaptability of fibers to accommodate a wide range of operating situations. Because the bristles slide against the rotor surface, 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 to develop reliable modeling techniques that can help identify complex relationships among brush seal design parameters, in-service load and contact forces that arise during operation of turbomachinery. The first portion of the current research 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 interference between the bristle/rotor and radial fluid flow, which is derived from aerodynamic forces termed "blow-down". In plane large displacement mechanics analysis was applied. Contact forces are obtained for a range of brush seal design parameters including fiber lay angle, flexural rigidity and length. The second portion of this research examines hysteresis , which is a major phenomenon that affects brush seal leakage and wear performance. Two mechanics models were developed to examine the hysteresis, namely, the role of distributed inter bristle friction force on hysteresis phenomenon and the bristle/back plate interaction model for assessing the hysteresis phenomenon. Nonlinear beam theory (2D) and general beam theory (3D) are applied for solving bristle deformation in the above two mechanics models, respectively. Hysteresis is quantified as the differential work done by friction force during a load cycle, and the consequence of hysteresis--"gapping" is explored as well. This systematic analysis of brush seal system is expected to provide valuable information for the development of new brush seals that exhibit improved performance, including reduced bristle/shaft wear, low hysteresis, and reduced leakage between successive stages of the turbine.

Recommended Citation

Zhao, Haifang, "Modeling, analysis and design considerations for brush seals used in turbomachinery" (2005). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI3172493.