Dynamic Characterization of Annular Gas Seals With 3D Printed Texture Patterns

Abstract

The rotordynamic characteristics and leakage are presented for three damper seals manufactured by 3D printing with carbon fiber reinforced Nylon. The seals have texture patterns consisting of diamond shaped holes. The first seal serves as a baseline and has consistent hole size over the length of the seal. The second seal has holes of varying size decreasing in the direction of flow. The final seal has constant hole size but has eccentric grooves whose radius is larger than the seal diameter in a manner reminiscent of multi-lobe bearings. Results were obtained at inlet pressures up to 19.3 bar-a (280 psia), rotor speeds of 10, 15, and 20 krpm, pressure ratios of 0.25, 0.35, 0.43 with and without inlet pre-swirl. Compared to the baseline seal, the variable hole size seal had larger direct stiffness and damping. At some conditions, the variable hole size seal had same sign cross-coupled stiffness which tends to distort the orbit rather than cause a destabilizing follower force. The cross-over frequency was lower for the variable hole size seal, but the advantage was reduced at 20 krpm. The leakage was reduced without pre-swirl, but the leakage with pre-swirl was not measured due to equipment failure. The eccentric groove seal displayed the largest leakage compared to the other seals, and reduced magnitude for all dynamic coefficients as a result of the increased average clearance caused by the eccentric grooves. All of the seals tested showed frequency dependence in both stiffness and damping.