Measured Rotordynamic and Leakage Characteristics of a Tooth-on-Rotor Labyrinth Seal With Comparisons to a Tooth-on-Stator Labyrinth Seal and Predictions

Rotordynamic and leakage data are presented for a see-through tooth-on-rotor (TOR) labyrinth seal with comparisons to a see-through tooth-on-stator (TOS) labyrinth seal. Measurements for both seals are also compared to predictions from XLLaby. Both seals have identical diameter and can be considered as relatively long labyrinth seals. The TOR seal has a length-to-diameter ratio of 0.62, whereas the TOS seal is longer and has a length-to-diameter ratio of 0.75. Both seals also differ by number of teeth, tooth height, and tooth cavity length. TOR labyrinth tests were carried out at an inlet pressure of 70 bar-a (1,015 psia), pressure ratios of 0.4, 0.5, and 0.6, rotor speeds up to 20,200 rpm, a radial clearance of 0.1 mm (4 mils), and three preswirl ratios. For comparison, TOS labyrinth tests were run at identical conditions as the TOR tests but for only one positive preswirl ratio. TOR labyrinth measurements show a pronounced dependence of rotordynamic coefficients on rotor speed, especially when compared to prior documented TOS labyrinth seal tests run at a radial clearance of 0.2 mm (8mils). The TOR labyrinth cross-coupled stiffness is higher in magnitude and increases at a higher rate than that of the TOS labyrinth across all test speeds. However, the TOR labyrinth effective damping was determined to be greater due to higher measurements of direct damping. Measured leakage rates for the TOR labyrinth were approximately 5–10% less than the TOS labyrinth. XLLaby underpredicted the rotordynamic coefficients for both seals. However, as with measurements, it predicted the TOR labyrinth to have higher effective damping than the TOS labyrinth.