69491 - Rotating Brush Seal Design and Performance Testing 

Brush seals are widely used in gas turbine, steam turbine and aviation engines because of their superior sealing effectiveness over labyrinth seals. Brush seals are usually mounted on the stationary components, and their flexible bristle tips engage the rotating component to form a dynamic seal. In this paper, a prototype with enhanced configuration is developed to study a brush seal attached to a rotating shaft. To achieve seal flexibility, the bristles are angled circumferentially, instead of axially, and are supported by a conical backplate. Under rotation, the bristles are pushed towards the backplate by the centrifugal force. The benefits of rotating brush seal include avoiding direct rub on rotor, which reduces heating to rotor and has less impact on rotor instability. Seal configurations are designed to fit into interstage and inter-shaft locations. A modeling approach for predicting stiffness and operating stresses in these seals also is outlined.

The benefits of rotating brush seals for turbomachinery include flexibility and sealing performance similar to stationary brush seal, but without direct heating to rotor. In this paper a number of different configurations for rotating brush seals are described. An efficient, cost-effective and precise manufacturing process for fabrication of the seals, using a helical drum manufacturing method is described, including embodiments involving welded bristles as well as core and clamping methods. Finally, a modeling approach for predicting stiffness and operating stresses in these seals has been outlined.

A flow rig is built at a sub scale level to test leakage performance and wear characterisitcs of rotating brush seals. The rig consists of a rotating flow rig with labyritth seal on one side of rotor, and brush seal on the other side. The leakage of labyrinth seal is subtracted from total leakage to calculate the rotating brush seal leakage. Static parts of different geometries are used for adjusting clearance of interference along the circumference of the rotating brush seal. Thermocouples are used to capture the heat generated due to friction.

Leakage testing of rotating brush seal is conducted at various pressures and speeds. Two stators are used: round and elliptical.  New seals showed excellent static clearance, and worn seal showed  higher static clearance, but the clearance rapidly reduces with increasing speed. At operational speeds, the worn seal shows promising dynamic clearance characteristics, with effective gaps almost similar to a new seal, indicating that the seal reaches an asymptotic wear rate, in which it doesn’t wear faster after initial rub in is done.