Experimental force coefficients for a two-bladed labyrinth seal and a four-pocket damper seal

Experiments are presented to identify the stiffness and damping force coeff icients of a two-blade, teeth on stator labyrinth seal with diverging clear ance and its modified version as a four-pocket gas damper seal. The seals I r ere tested without journal rotation and at rotor speeds of 1500 rpm and 3 000 rpm for seal supply to ambient pressure ratios ranging from 1 to 3. Cal ibrated impact loads excite a flexible supported housing holding rigidly th e test seal. The impact loads and seal displacement and acceleration time r esponses are measured and recorded as frequency spectra. The instrumental v ariable filter method is used to identify the seal dynamic force coefficien ts from the measured transfer functions over a frequency range. The experim ents demonstrate the four pocket gas damper seal has large (positive) direc t damping coefficients and relatively small (negative) direct stiffness coe fficients. The two bladed labyrinth seal exhibits positive direct stiffness and negative damping force coefficients. The leakage performance of both s eals is nearly identical. The four pocket damper seal clearly outperforms t he labyrinth seal in terms of rotordynamic forces. Both seals show a minima l amount of cross-coupling force effects, well within the experimental unce rtainty.