Non-linear Analysis of Floating Ring Annular Seals: Stability and Impacts

Floating ring annular seals represent one of the solutions for controlling leakage in high speed rotating machinery. Low leakage is ensured by the small radial clearance. Under normal operating conditions, the ring must be able to “float” on the rotor in order to accommodate its vibration. Impacts between the carbon ring and the rotor are prohibited. The present paper introduces a non-linear numerical model of gradually increasing complexity. A first version of the model has two translation degrees of freedom and describes planar trajectories of the floating ring. It uses transient hydrodynamic and Coulomb forces. The next step is including impacts between the rotor and the carbon ring and between anti-rotation pins and the ring casing. A rotation degree of freedom must be also added. The results show that for a given rotation speed and with increasing amplitude of the rotor whirl, the trajectory of the floating ring seal changes from uniform whirl to quasi-periodic before triggering contacts in the main seal. The impacts of the anti-rotation pins with the ring casing completely modify the dynamic response.