Stiffness and friction characterization of brush seals

Official URL: http://risc01.sabanciuniv.edu/record=b1534425 (Table of Contents)

Improvements in steam and gas turbine technologies constantly drive harsher conditions, which result in thermodynamic cycles having higher pressure ratios and inlet temperature levels as well as increased leakage flows. Necessity of reducing the internal leakage flows and thermodynamic cycle losses while increasing the turbine overall efficiency puts greater importance on improvements in sealing technologies. Labyrinth seals have been used almost since the invention of gas turbines and their technology is very well developed over the years. However, leakage rates are still not satisfactory and cannot meet the performance requirements of new generation turbines. Brush seals are fulfilling the leakage performance requirements and they can successfully compensate rotor interference at turbine transient conditions. Due to their superior and stable leakage performance and compact size, brush seals are replacing traditional labyrinth seals at critical sections of turbines. A brush seal consists of a series of bristles which rub on the shaft surface. Since the bristles slide against the high-speed rotating shaft, friction and wear at the bristle tip contact becomes a major concern as it determines the life and efficiency of the seal and also rotor stability. Evaluating bristle tip contact forces and resulting stress levels at operating conditions is critical to optimize the seal performance and safety. A brief literature survey reveals the lack of test data and analysis methods for evaluating seal stiffness and stress levels at operating conditions. In an attempt to meet this need, custom test rig design and methodology has been developed to perform stiffness tests at turbine operating conditions. Analytical studies and finite element simulations have been performed for test seals and results have been correlated with the test data of this study. Furthermore, stiffness and friction characterization of brush seals has been conducted through correlated FE models, and MATLAB based code has been developed for automatic brush seal FE model generation for ABAQUS simulations.