A comparison of the static and dynamic characteristics of straight-bore and convergent tapered-bore honeycomb annular gas seals

Abstract

Results are presented from tests conducted with straight-bore and convergent tapered-bore honeycomb annular gas seals. The test seals had a 114.3 mm bore with an L/D = 0.75 and a nominal radial clearance of 0.19 mm. The honeycomb cell depth for both seals was 3.1 mm and the cell width was 0.79 mm. Static and dynamic measurements are reported with air at three speeds out to 20,200 rpm, three supply pressures out to 17.2 bar, and with exit-to-inlet pressure ratios of 40% and 60%. The results demonstrated that the convergent tapered-bore honeycomb seals exhibited significantly larger (73%) effective stiffness and had significantly less effective damping (71%) compared to the straight-bore honeycomb seals. The convergent tapered-bore honeycomb seals leaked an average of 48% more than the straight-bore honeycomb seals. The dynamic impedance measurements show that the honeycomb seals do not fit the conventional frequency-independent model for annular gas seals. Numerical predictions from a computer program incorporating the new two-control-volume model of Kleynhans and Childs (1997) correlate well with both measured seal leakage and dynamic impedance for the honeycomb seals. Predicted leakage rates varied less than 11% and 18% of the measured straight-bore and convergent tapered-bore honeycomb seal leakage measurements respectively. In general, impedance predictions correlated well with both honeycomb seals across all of the test cases. Better correlation was observed at higher speed and higher inlet pressure for both honeycomb seals, with the straight-bore honeycomb seal predictions correlating best with the measured data.