MEASUREMENTS OF THE LEAKAGE AND ROTORDYNAMIC PERFORMANCE OF INTERLOCKING LABYRINTH SEALS

Leakage and rotordynamic measurements are presented for an interlocking-labyrinth gas seal. Magnetic bearings and differential-pressure transducers are used to measure dynamic forces in the labyrinth seal following the approach of Wagner et al. in 2009. Magnetic bearings precess the rotor creating a dynamic pressure wave that is measured and integrated to find the reaction forces. The interlocking seal has 3 teeth on the stator and 2 teeth on the rotor creating 4 cavities. Each cavity has an axial length of 6 mm, and all teeth have a 5 mm height. Teeth on the rotor and stator, respectively, create a 0.2 mm radial clearance with respect to the stator and rotor. All tests are conducted at similar to 167 Hz (10 krpm) rotor speed with, and without, swirl brakes for a range of precession frequencies from 10 50 Hz forward and backward. Inlet pressure is varied between 2.75 4.83 bar, and pressure ratios vary between 0.5 similar to 0.8. Static results are presented for leakage, inlet preswirl, and cavity pressure. Dynamic results are presented for rotordynamic coefficients. Dynamic results show behavior that is unique to each cavity and are presented for the entire seal as well as for each cavity individually. Cross-coupled stiffness of the entire seal increases with increasing precession frequency, yet all other rotordynamic coefficients are frequency independent. The seal shows improved stability via increased effective damping with the use of swirl brakes when considering the entire seal. Negative direct damping values are seen in all but the third cavity.