Operational Modal Analyses of Brush Seals and Seating Load Simulations

Abstract

Brush seals are one of the most effective sealing technologies in turbomachinery since they enable contact-type operation for close clearance control. Brush seal bristles must interact under turbine conditions, and the minimum pressure load to initiate proper contact between fibers is called seating load. Seating load evaluation is essential for the durability and stability assessment of bristles since unseated fibers may flutter and cause seal failure. Even with proper seating, brush seal critical modes may still be excited by flow-induced fluctuations or bucket tip excitations. In this study, a finite element-based methodology was developed to determine the seating load and identify the critical modes of brush seals. Under pressure load, brush seal nonlinear contact simulations are followed by frequency-based analysis to determine bristle and seal pack critical modes. To determine the seating load of the brush seal, the change in modal response is examined. In this paper, the modeling methodology, parameter correction procedures, geometric inspection of test seals, correlation of transient analyses with dynamic tip force measurements, operational modes of brush seals and seating load evaluation methods are detailed.