University of Bath

A fundamental investigation into brush seal fluid dynamics

This project aims to improve the fundamental understanding of brush seals by making measurements in large-scale, simplified experiments.

Brush seals are one example of a type of shaft-seal used within gas turbine engines. They contain a static ring of densely packed fine wire bristles (usually metallic) angled in the direction of rotation of the component. This provides a high resistance to flow and allows them to maintain a pressure drop. This type of seal allows for very low leakage, making it an attractive option for gas turbine designers.

The benefits of using brush seals in gas turbines have long been known. But their use in aerospace applications has been limited because of rapid deterioration of in-service performance. Fluid dynamic mechanisms such as bristle blow-down and pressure stiffening are responsible for the rapid wear. We need to have a better understanding of these effects. This will allow us to exploit the benefits and use brush seals more throughout gas turbines.

Brush seals are typically modelled theoretically using a porous medium approach. 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.

Our project aims to improve the fundamental understanding of brush seals. And it will provide validation data for porous media models by making measurements in large-scale, simplified experiments. We are collaborating with Cross Manufacturing Ltd on this project. They are a world-leading supplier of brush seals to the gas turbine industry. The insight we gain will form a database to be used to design brush seals in the future. This will have impact not only for Cross but also for the wider gas turbine industry.