Test results for liquid "damper" seals using a round-hole roughness pattern for the stators

Test results are reviewed for two annular liquid seals (L = 34.9 mm; D = 76 .5 mm) at two clearances (.1 and .12 mm), The seal stators use hole-pattern -roughened stators that are identical except for hole depths of .28 and 2.0 min. Tests are conducted at three speeds out to 24,600 rpm and three press ures out to 68 bars, Test delta consist of leakage rates and rotordynamic c oefficients at centered and eccentric positions with static eccentricity ra tios out to 0.5. Test results are consistent with expectations in regard to the reduction of cross-coupled stiffness coefficients due to stator roughn ess. However, the measured direct stiffness coefficients rr ere unexpectedl y low. A partial explanation for these results is provided by measured fric tion factor data which show an increase in the fr friction factors for pres sure-driven flow with an increase in clearance. A prediction model for roto rdynamic coefficients, incorporating the friction-factor data, predicted a substantial loss in direct stiffness bur could not explain the very low (or negative) values that were measured. The model did explain the measured dr op in cross coupled stiffness (k) and provides an alternative explanation t o observed reductions in k values; specifically, an increase in the frictio n factor with increasing clearance causes a reduction in k irrespective of any parallel reduction in the average circumferential velocity.