Rotordynamics and Fluid Seals

The residual leakage flow through the non-contacting seals leads to forces that can destabilise the stationary rotor movement, if certain operating speeds are exceeded. The consequences can be unwanted or intolerable noise or vibrations, or even rotor damage.

In recent years, sealing designs including structural compliance have been investigated (HALO-Seal [SanAndres2015], GLAND-Seal [Messenger2015]). A compliant design can reduce the sealing gap between the rotor and the housing, while at the same time allowing the seal to follow rotor movements and thus mitigate pressure build-up in the leakage flow. This may stabilise the stationary rotor movement.

At the Engineering Dynamics working group, the influence of compliance in seals on rotor dynamics is investigated theoretically.

Various theoretical models of varying complexity and associated experiments are set up to investigate the effect of compliance in seals. The linear and nonlinear behaviour is considered.

The simplest model stage consists of a Laval rotor, a visco-elastically supported seal and a leakage flow. The force effect of the leakage flow is either described by the Muszynska model [Muszynska1988] or determined by simulating the leakage flow using the bulk flow equations. The system shows improved stability properties and complex bifurcation behavior, where stable and unstable periodic synchronized limit cycles, as well as unstable quasi-periodic attractors occur.