Methodology for Counter Torque, Power Loss, and Frictional Heat for Brush Seals Under Eccentric Transients

Abstract

Turbomachinery brush seals are used for achieving close clearance control with the aid of flexible bristles. Frictional forces between bristle tips and rotor surfaces induce counter torque, power loss, and heat generation during turbomachinery transients; all of these determine the overall efficiency, operation life, and stability of turbomachinery application. As a result of manufacturing tolerances, rotor dynamics-induced shaft deflections, and additional gyroscopic loads in aviation engines, eccentric rotor rub occurs toward brush seals in transients, causing partial rotor–seal contact with nonlinear radial interference and uneven tip force distribution. There is an inherent error in the current power loss and frictional heat rate analyses, as well as in counter torque methodologies, since they do not account for the uneven tip force distribution. In this study, a nonlinear radial interference profile of eccentric rotor contact conditions has been derived and its effect on contact angle has been examined with a comparative analysis with concentric rotor expansion. The methodology for counter torque, power loss, and generated frictional heat rate analyses has been detailed, and eccentric condition formulations have been derived with the surface integration of dynamic bristle tip force functions adopted from brush seal dynamic stiffness tests. Analysis of nonlinear interference and uneven contact force profiles has been conducted based on the combined effects of assembly conditions and eccentricity levels. Results obtained using the developed closed-form equations for eccentric rotor contact are compared with concentric rotor expansion and simple eccentric rotor rub analyses, which do not account for uneven tip forces.