Hybrid brush pocket damper seals for turbomachinery

Pocket damper seals perform a dual function: both sealing the pressurized g as around a rotating shaft and providing large amounts of vibration damping , The annular cavity between the labyrinth seal teeth is subdivided into se parate annular cavities around the circumference of the rotor by partitioni ng walls. Also, the upstream and downstream teeth have different radial cle arances to the rotor. These seals have been shown to provide a remarkable a mount of direct damping to attenuate vibration in turbomachinery, but they generally leak more than conventional labyrinth seals if both seals have th e same minimum clearance. Conversely, brush seals allow less than half the leakage of labyrinth seals, bur published test results show no significant amount of damping, They are considered to be a primary choice for the seals in new aircraft engine designs because of their low leakage. This paper wi ll describe a recently invented hybrid brush/pocket damper seal that combin es high damping with low leakage, Previous brush seal results were studied and calculations were made to select a brush seal to combine with the pecke r damper design, The result is a hybrid seal with high damping and low leak age. A special design feature can also allow active vibration control as a bonus benefit, A computer code written for the original pocket damper seal was modified to include the brush element at the exit blade, Results from t he computer code indicate that the hybrid seal can have less leakage than a six bladed (or 6 knives) labyrinth seal along with orders of magnitude mor e damping, Experimental evaluations of the damping and leakage performance of the hybrid seal are being conducted by the authors. The experimental wor k reported here tested the damping capability of the new hybrid brush seal by exciting the seal journal through an impedance head, A conventional six- bladed labyrinth seal of the same working dimensions was also tested. The b rush hybrid pocket damper seal is found to leak less than the labyrinth sea l while producing two To three times more damping than the original pocket damper seal (orders of magnitude more than the conventional labyrinth).