Abstract
Sealing in gas turbines is paramount to overall performance and efficiency. Brush seals offer superior performance compared to other sealing solutions commonplace in modern turbomachinery. When subjected to a pressure load, a ring of flexible fine wire bristles — fitted at a lay angle to the radial plane — compact to resist the oncoming flow and deflect towards the rotor in a process known as blow-down. This study employs Digital Image Correlation to track individual bristle tips in three spatial axes throughout a large-scale brush seal test facility. This is the first-time direct measurements of blow-down throughout the bristle pack have been presented, providing a unique insight into the mechanical behaviour of brush seals.
Increased magnitudes of blow-down and axial bristle deflection were demonstrated in upstream bristle rows and at larger clearances. Analysis of these results in conjunction with the interrogation of the inter-bristle pressure field proved that blow-down is more prevalent for pressure relieving brush seals in comparison to conventional configurations. The reduction in the through-flow clearance area resulted in a significant enhancement in sealing performance for a clearance seal, highlighting a key advantage of the pressure relieving back plate design.
