Numerical investigations on the rubbing process in labyrinth seals for full flight mission [in press]

Labyrinth seals are a commonly used sealing technology to prevent and control leakage flows at rotor-stator interfaces in turbo machinery. Small clearances required by higher pressure ratios and the economical use of cooling air lead to potential rubbing events. These may cause detrimental heat input into the rotating structure and can lead to severe damages. Honeycomb liners on the stator part tolerate rubbing events to a certain extent and therefore allow for smaller gap widths, which lead to minimal leakage. A unique and independently developed one-dimensional numerical model is used to investigate critical rubbing conditions in a typical aircraft flight mission. It considers kinematic contact conditions, friction, heat conduction and abrasive and plastic wear. This model allows the calculation of the loads, such as the contact pressures and temperatures on the components. First experimental investigations for an idealized contact between a metal foil, representing the honeycomb part, and a rotating seal fin are used to validate the model. Then, predictions of engine performance calculations are additionally used to calculate input parameters for the one-dimensional model. These are the relative contact velocity and the casing temperature of the honeycomb. Finally, the results of the one-dimensional rubbing model such as rub forces, temperatures and wear of the seal fin or the honeycomb liner are compared for five different operating points of the flight mission: Ground idle, Takeoff, Cruise, Approach, Re-slam. Based on these results, damaging effects on the sealing system are evaluated and the most critical operating point, in this case the Re-slam, could be identified.