Fluid Dynamic Behaviour of Conventional and Pressure Relieving Brush Seals

Brush seals consist of a static ring of densely packed, flexible, fine wire bristles that provide resistance to the flow. Pressure relieving brush seals can be employed to overcome issues such as hysteresis that affect seal durability by reducing friction between the bristle pack and back plate surface. The impact of such designs on the fluid dynamic behaviour of brush seals was studied following a concomitant methodology that exploited the benefits of both engine representative and large-scale testing facilities. Leakage data were fitted using a porous medium model found in the literature to quantify viscous and inertial resistance coefficients. Shaft rotation was shown to cause a reduction in seal leakage and an increase in static pressure on the back plate surface. The pressure relieving back plates also resulted in increased static pressures at this location, causing a reduction in flow resistance that increased leakage through the porous bristle pack. Interrogation of the large-scale inter-bristle pressure field for the two back plate designs revealed the distributions of axial pressure diverged towards the rear of the bristle pack. The detail gathered using the large-scale study has been shown to be representative, hence the insight is generically applicable to brush seals.