Rotordynamic Characteristics for A Tooth-On-Rotor Long Labyrinth Seal Using Computational Fluid Dynamics

The paper compares experimentally derived dynamic force coefficients for a tooth on rotor (TOR) labyrinth seal (LS) against predictions obtained from URANS (Unsteady Reynolds Averaged Navier-Stokes) Computational Fluid Dynamics (CFD) simulations and a one control volume (1CV) Bulk Flow Model (BFM). With 14 teeth and radial clearance CS= 0.1016 mm, the test LS has diameter D = 114.3 mm and overall length L = 0.62 D, as stated by Arthur and Childs [1] The seal, supplied with pressurized air at inlet pressure Pin= 50 bar and ambient temperature, operates with rotor speed of 20.2 krpm, and is set to an exit to inlet pressure ratio = 0.4. The CFD analysis applies a simultaneous multiple-frequency excitation method [2] to extract the rotordynamic force coefficients. The CFD predicted force coefficients show good correlation with the experimental force coefficients, albeit the predicted LS leakage is ~14.5% greater than the recorded flow. Note the experimental set-up includes upstream and downstream uniform clearance sections which affect considerably the evolution of the circumferential swirl entering the LS section. The upstream and downstream plain annular seal sections do affect the test element (estimated) cross-coupled stiffness (30% of overall) and direct damping coefficients (40% of overall). The study further compares the results of a 1CV BFM against the CFD predictions and the experimental results. The simple BFM underpredicts the seal crosscoupled stiffness and direct damping even when implementing the static pressure and inlet swirl condition derived from the CFD flow field.