Dynamic force coefficients of a multiple-blade, multiple-pocket gas damperseal: Test results and predictions

Experimental rotordynamic force coefficients and leakage for a four-blade, two-four pecker gas damper seal are presented and compared to predictions b ased on a one control volume bulk-flow model. The test rig comprises a vert ical shaft and a test seal housing and flexible structure suspended from a rigid centering frame. The experiments were conducted at increasing rotor s peeds to 6000 rpm and inlet/exit pressure ratios from 1.0 to 3.0. The seal force coefficients are obtained from impact response measurements of the se al and flexible structure using a frequency domain parameter identification technique. Both measurements and predictions show the seal direct stiffnes s and damping coefficients are proportional to the inlet/exit pressure rati o and insensitive to rotor speed. The agreement between experimental result s and analytical predictions is acceptable. Predicted cross-coupled stiffne ss coefficients are of small amplitude. However, the test results evidence cross-coupled stiffnesses without journal rotation due to a structural asym metry induced by the external pressurization into the seal.