Rotordynamics of a Single-Stage Brush Seal in Isolation: The Effects of Variable Stiffness and Back Plate Geometry

Abstract

Brush seals control leakage around rotating components from areas of high to low pressure inside turbomachinery. They are known to contribute to the overall stability of gas turbines, therefore their dynamic behaviour is of particular importance to engine designers. Despite this, limited research exists in the literature on the rotordynamic behaviour of brush seals. This paper aims to experimentally characterise the leakage and rotordynamic performance of two seals with different bristle diameters tested with both conventional and pressure-relieved back plates with a slight interference. A dynamic test facility was utilised to study the dynamic characteristics of an isolated seal with changes in excitation frequency, rotational speed and pressure drop. Seal leakage increased with bristle diameter and with the use of the pressure-relieved back plate but reduced with increasing rotational speed for all tests. The direct dynamic coefficients were shown to increase with pressure difference. The back plate geometry influenced the change in stiffness coefficient with rotational speed. The larger bristle diameter resulted in a stiffer seal, however, the damping coefficient reduced with the reduction in packing density. The insight provided by these results will help inform engine manufacturers on the suitability of implementing brush seals in future gas turbine designs.