Numerical Investigation on Windback Seals Used in Aero Engines

Abstract

Seals are considered one of the most important flow elements in turbomachinery applications. The most traditional and widely known seal is the labyrinth seal but in recent years other types like the brush or carbon seals were introduced since they considerably reduce the sealing air consumption. When seals are used for sealing of aero engine bearing chambers they are subjected to high "bombardment" through oil particles which are present in the bearing chamber. These particles mainly result from the bearings as a consequence of the high rotational speeds. Particularly when carbon or brush seals are used, problems with carbon formation (coking) may arise when oil gets trapped in the very tight gap of these seals. In order to prevent oil migration into the turbomachinery, particularly when the pressure difference over a seal is small or even negligible, significant improvement can be achieved through the introduction of so called windback seals. This seal has a row of static helical teeth (thread) and below this thread a scalloped or smooth shaft section is rotating. Depending on the application, a windback seal can be used alone or as a combination with another seal (carbon, brush or labyrinth seal). A CFD analysis carried out with ANSYS CFX version 11 is presented in this paper with the aim to investigate this seal type. The simulations were performed by assuming a two-phase flow of air and oil in the bearing compartment. Design parameters like seal clearance, thread size, scallop width, were investigated at different operating conditions.

Influence of Shape, Installation and Rotation Motion Errors on Tin Bronze Clearance Seal of Rotary Joint

“…The rotary joint, as a connecting piece for transporting fluid medium from the fixed pipeline to the rotating pipeline, can realize the transmission of sealed medium under the condition of high pressure and high speed, and is widely used in military, aerospace, hydraulic and pneumatic transmission and other fields [1,2]. Rotary joints generally use the clearance of matching parts to achieve sealing effect, but the size of the clearance will have an impact on the overall performance of the rotary joint.…”

Influences of the Geometry of the Scavenge Pipe on the Air–Oil Two-Phase Flow and Heat Transfer in an Aero-Engine Bearing Chamber

“…A further research indicates that although the screens reduce the parasitic losses and vent protrusion reduces the oil flow to the air–oil separator, the high-temperature problems caused by the oil flow distribution may lead to malfunctions in the engine’s lube system . In addition, sealing has an impact on the air–oil two-phase flow and heat-transfer performance. − Compared to the vent pipe, the scavenge pipe carries away most of the oil from the bearing chamber. The high-temperature oil inevitably involves a small amount of high-pressure sealing air and forms a complex air–oil two phase flow, which may lead to oil coking and oil fires. , …”