Fluid Structure Interaction (FSI) in Labyrinth seals of Jet Engines

Labyrinth seals are widely used in gas turbine engines to control internal leakage, thereby increase engine performance and decrease operating costs. To provide sealing across a stationary/ rotating interface, labyrinth seals have to be non-contacting to avoid excessive heat production. However, their sealing capacities are limited by the need to maintain a clearance between the seal and the rotating surface. Hence improving sealing performances is equivalent to minimizing leakages while preventing any forms of contact in seals, where the interaction between the leakage flow and the seal structure plays a dominant role. Such problems are known as the Fluid Structure Interaction (FSI) problems. Therefore, FSI needs to be employed in numerical simulations to accurately represent the coupled physics in labyrinth seals.

From a numerical point of view, FSI means the combination of Computational Fluid Dynamics and Computational Solid Mechanics to solve the coupled fluid and solid fields. It is an important branch of multi–physics analysis, and is applied when the physics is more complex than a single field analysis can simulate. FSI has attracted many researchers and has become a major focus in the field of computational engineering over the past years.

This project is focused on the numerical simulation of the two-way mechanical and thermal FSI in labyrinth seals. Fluid force induced vibration, heat transfer across the fluid-solid surface, as well as rotationally induced inertial effects are investigated using FSI. The fluid solver ANSYS® CFX® and the structural solver ANSYS® Mechanical™ are coupled implicitly without any third-party interface.

In the case of fluid force induced vibration, a non-rotating room temperature straight-through labyrinth seal was simulated. We found out that the amplitude of the rotor is linearly dependent on the pressure ratio and mass flow as in Fig. 3 and Fig.4. In addition, we established an approach to obtain proper initial conditions and investigated their influence on the results. We would like to point out that the computations were run in parallel on an IBM p 575 SMP cluster with POWER6 nodes.

In the case of heat transfer across the fluid-structure surface and the case of rotationally induced inertial effects, we used a rotating stepped labyrinth seal. First the fluid model was verified and validated against experimental measurements as in Fig. 5. Then the FSI results were compared to the single field results, showing that FSI does have a significant influence on the numerical simulations. Next, a systematic parameter study will be conducted employing FSI with respect to the seal geometry and various operating conditions.

The FSI effects in labyrinth seals are determined directly without any simplifications or empirical assumptions, which cannot be achieved by single field approaches. Thereby the complex coupled physics is numerically investigated with a greater accuracy as well as a greater flexibility.

Multi-Physics; Special Coupled Systems: Fluid-, Thermo- and Structural Dynamics

Yu Du

M.Sc.

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