Experimental rotordynamic coefficient results for (a) a labyrinth seal with and without shunt injection and (b) a honeycomb seal

摘要

Centrifugal compressors are increasingly required to operate at higher pressures, speeds, and flu id density. In these conditions, compressors are susceptible to rotordynamic instabilities. To remedy this situation, labyrinth seals have sometimesbeen modified by using shunt injection. In shunt injection, the gas is taken from the diffuser or discharge volute and injected into an upstream chamber of the balance-piston labyrinth seal The injection direction can be radial or against rotation. Thisstudy contains the first measured rotordynamic data for labyrinth seals with shunt injection. A comparison has been made between conventional labyrinth seals, labyrinth seals with shunt injection (radial and against rotation), and a honeycomb sealLabyrinth seals with injection against rotation are better able to control rotordynamic instabilities than labyrinth seals with radial injection; however, the leakage is slightly higher. The leakage comparison for all seals demonstrates that the honeycomb seal has the best flow control Test data are presented for a top rotor surface velocity of 110 m/ sec, a supply pressure of 13.7 bars, and Ipr=0.95 (injection pressure is 1.05=1/ 0.95 times the seal inlet pressure). For these conditions, and consideringeffective damping, the labyrinth seal with injection against rotation is better than the honeycomb seal when the pressure ratio across the seal PR 0.45. The effectiveness of theshunt-injection against rotation in developing effective damping is reduced with increasing rotor surface velocity.