Rotordynamics and Fluid Seals


Steam turbines, aircraft engines, centrifugal pumps or turbochargers are just a few popular examples of systems in which rotors interact with compressible or incompressible fluids. The energy conversion in these machines is usually based on a build-up or reduction of pressure. Leakage between volumes of different pressures along the rotor is reduced by means of fluid seals. Non-contact seals allow relative movement of rotor and housing while minimising wear.


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.

Methodology and Phenomena

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.




Bifurcations: radii of periodic and mean radii of the quasi-periodic limit cycles of the rotor (solid) and the seal (dotted). Red: Stable. Grey: Unstable. Blue: Quasi-periodic