Finger seal solid modeling design and some solid/fluid interaction considerations

The technology of shaft compliant seals was revolutionized when brush seals first replaced the labyrinth seals at many locations along compressor and turbine shafts. Finger seals present a compliant seal alternative to brush seals and through their geometric configuration bring about the added potential of hydrodynamic lifting and thus non-contacting operational features. Their manufacturing costs are well below those of brush seals and their potential lifting capability, by eliminating the wear factor, increases considerably their life span while making them a preferred embodiment to brush seals. The fingers' compliance allows both axial and radial adjustment to rotor excursions without damage to the integrity or performance of the seal. The work to be presented here concerns design development through numerical simulation of the motion of an assembly of two high pressure (HP) and one low pressure (LP) fingers arranged axially in a staggered configuration and subject to an axial pressure drop. This combination of fingers represents the smallest repetitive basic elemental cell component of a Finger Seal (FS). The numerical 3-D results presented herein were obtained using customized commercial packages. The solid models using ALGOR as the computational engine study the deformations and stresses of the finger(s) and its/their lifting capabilities. The integrated numerical approach coupling the hydrodynamic fluid model (Navier-Stokes based) to the solid fingers deformation and motion (CFD-ACE+ and FEMSTRESS) allows calibration of the floating and sealing capabilities of the FS at the same time. The entire study is aimed at generating reliable design procedures for the parametric design of a finger seal.