A Study of the Effects of Inlet Preswirl on the Dynamic Coefficients of a Straight-Bore Honeycomb Gas Damper Seal

Honeycomb seals are frequently used as replacements for labyrinth seals in high-pressure centrifugal compressors to enhance rotordynamic stability. A concern exists that this enhanced stability will be lost if the honeycomb cavities become clogged. Static and dynamic tests were conducted on a honeycomb and a smooth seal (representing the honeycomb seal with completely clogged cells) at the same constant clearances using air with a supply pressure of 70 bars. The test matrix included three speeds, three pressure ratios, and three inlet preswirl conditions. The results show increased leakage, decreased synchronous stiffness, and decreased dynamic stability for the smooth seal with preswirled flow. The results strongly support the use of swirl brakes at the entrance of a honeycomb seal if clogging is a concern. Comparisons between test results and predictions from a two-control-volume theory by Kleynhans and Childs showed excellent agreement in general.