Thermofluids considerations and the dynamic behavior of a finger seal assembly

Finger seals represent a compliant seal configuration. What differentiates and makes them preferable to the brush seats is their potential hydrodynamic lifting capabilities, and thus their noncontacting nature. The fingers' compliance allows both axial and radial adjustment to rotor excursions without damage to the integrity of the seal. The work to be presented here concerns the mapping of the thermofluid and dynamic behavior of a repetitive section of the newly proposed design of a two-layer finger seal. The assembly contains four high-pressure and four low-pressure fingers arranged axially at a staggered configuration and subject to an axial pressure drop. The numerical three-dimensional temperature and pressure results were obtained using a customized Navier-Stokes-based commercial package, CFD-ACE+. The results were obtained in a parametric fashion where the high-pressure side, the speed of rotation, and the heat transfer coefficient are the controlling parameters,the gas compressibility and the viscosity are also considered in the model of the thermofluids seal behavior. The stiffness and damping characteristics of the padded/unpadded fingers and the fluid were obtained through numerical simulation and were then used to model the interaction with the motion of the shaft. It is shown that the proposed geometry provides satisfactory lifting capability for the fingers. The fingers follow the motion of the shaft and their stiffness is small when compared to that of the fluid; thus, the displacement transmissibility is in most cases close to 1. Lifting forces and seal leakages, as well as the interaction between the profiled backplate and the low-pressure fingers through Coulomb damping/friction forces, are also parametrically studied.