Dynamic Forces From Single Gland Labyrinth Seals: Part II—Upstream Coupling

The standard lumped parameter model for flow in an eccentrically offset labyrinth seal, which assumes constant upstream and downstream boundary conditions, has been extended to include the effects of a nonuniform upstream cavity flow due to coupling. This new model predicts that the upstream perturbations in pressure and azimuthal velocity caused by this coupling can have a very strong impact on the pressure distribution in the seal gland itself. Augmentation by a factor of four, over the uniform inlet model, is predicted under some circumstances. Although no precise comparison to the experimental data with this new model was possible, due to the lack of control over the face seal venting the upstream cavity to the center hub plenum, the calculated effect of this coupling was shown to be approximately what was required to restore quantitative agreement between the data and theory. The new theory can explain the anomalously large pressure nonuniformity previously found by other authors in short seals as well as the first few glands of multicavity seals.