A bulk-flow analysis of multiple-pocket gas damper seals

A bulk-flow model for calculation of the dynamic force characteristics in a single cavity, multiple-pocket gas damper seal is presented. Flow turbulen ce is accounted for by using turbulent shear stress parameters and Moody's friction factors in the circumferential momentum equation. Zeroth-order-equ ations describe the isothermal flow field for a centered seal, and first-or der equations govern the perturbed flow for small amplitude rotor lateral m otions. Comparisons to limited measurements from a four-pocket gas damper s eal show the current model to predict well the mass flow rate and the direc t damping coefficient. For a reference two-bladed teeth-on-stator labyrinth seal, the current model predicts similar rotordynamic coefficients when co mpared to results from a two control volume, bulk-flow model. Force coeffic ients from a reference single-cavity, Sour pocket gas damper depend on the rotor speed and pressure drop with magnitudes decreasing as the rotor whirl frequency increases. The multiple-pocket gas damper seal provides substant ially more damping than a conventional labyrinth seal of the same dimension s. The damper seal cross-coupled stiffness coefficients are small though se nsitive to the inlet circumferential preswirl flow.