Transient Temperature Measurements in the Contact Zone Between Brush Seals of Kevlar and Metallic Type for Bearing Chamber Sealing Using a Pyrometric Technique

Abstract

For the past 25 years brush seal technologies have evolved into the aero engine designs and, more generally, into the gas turbine world, not only for sealing gas areas at different pressure levels but also for sealing gas/liquid environments. This is the case in an aero engine where the bearing chambers are sealed. Aero engine bearing chambers enclose oil lubricated components such bearings and gears. In order to avoid contamination of the turbo machinery through oil loss, air blown seals are used to retain the oil into the bearing chamber. Oil loss may cause coking or ignition with the probability of an uncontained destruction of rotating parts such as disks or blades. It may also cause contamination of the air conditioning system with oil fumes thus causing health problems to the passengers and crew from such exposure. The most widely known seals for bearing chamber sealing are the labyrinth seals, however, in recent years brush seals and carbon seals have also been used. The latter are contact seals; that is, they may be installed having zero clearance to the rotating part and lift during operation when their air side is pressurized. During this survey an actual aero engine bearing chamber was modified to run with brush seals in a simulating rig. Two types of brush seals were used: (a) with bristles made of Kevlar, and (b) bristles made of a metallic material. Both types were installed with an overlap to the rotor. The targets set were twofold: (a) to measure the transient temperatures in the rotor and particularly in the contact zone between the bristles and the rotor, and (b) to measure the air leakage through the seals at different operating conditions. In order to obtain the transient temperature measurements with high fidelity, a new pyrometric technique was developed and was applied for the first time in brush seals. This technique has enabled placement of the pyrometer into the bristle's pack of the seal adjacent to the rotating surface and it could record the frictional temperature evolution in the bristles/rotor contact zone during acceleration or deceleration of the rotor. Additionally, the air consumption of the seals was measured and was compared to the air consumption through the labyrinth seals. For the metallic brush seal, up to 80% of the required sealing air can be saved, which can result, in turn, into a reduction in fuel burned by up to 1%. Furthermore, a design simplification of the bearing chamber architecture can be achieved by taking into account the reduced air flow. Even though the rotor was accelerated to high speeds up to 19,500 rpm, the produced temperature overshoots in the seal/rotor contact zone have caused no deterioration in either the materials or the oil.