A Fundamental Investigation into Brush Seal Fluid Dynamics

Brush seals are one example of a type of shaft-seal used within gas turbine engines. They maintain a pressure drop by virtue of the high resistance to flow provided by a static ring of densely packed, fine wire bristles (usually metallic) that are angled in the direction of rotation of the component. Very low leakage is possible with this type of seal making it a highly attractive option for gas turbine designers. Although the benefits of using brush seals in gas turbines have long been established, their utilisation in aerospace applications especially has been limited due to the rapid deterioration of in-service performance. Fluid-dynamic mechanisms for this rapid wear have been identified such as bristle blow-down and pressure stiffening. For brush seals to be implemented more readily throughout gas turbines and to allow the potential benefits to be exploited, a greater understanding of these effects is required. Brush seals are typically modelled theoretically using a porous medium approach where the influence of the seal on the flow is defined by a set of resistance coefficients. These coefficients have to be calibrated using experimental data to enable correct extrapolation to engine conditions. There is currently a distinct lack of published experimental values available in the literature. This proposal aims to improve the fundamental understanding of brush seals and provide validation data for porous media models by making measurements in large-scale, simplified experiments. The programme will be conducted in close collaboration with Cross Manufacturing Ltd., a world-leading supplier of brush seals to the gas turbine industry. The insight obtained will provide a database which will be used to inform the design of future brush seal configurations, not only by Cross but also the wider gas turbine industry.