EFFECT OF PARTIAL ADMISSION AND SWIRL BRAKES ON DESTABILIZATION FORCE OF LABYRINTH GAS SEAL

Destabilization forces in labyrinth seals can cause subsynchronous vibration and many researchers have investigated the destabilization force under full admission (FA). It is known that partial admission (PA) can increase rotor instability, but there is little knowledge about seal fluid force under PA. In this study the experiment was conducted in order to confirm the effect of PA and swirl brakes (SB) on swirl velocity and destabilization force. For the experiment, a 500mm diameter rotor was used so that size of the labyrinth seal can be close to the large-scale steam turbine. According to the experimental results, it was found that (1) average swirl velocity and destabilization force under PA became larger than FA, (2) relationship between average swirl velocity and destabilization force under PA was almost same with that of FA, (3) seal fluid force under PA had anisotropy by the instant rotor position, (4) SB reduced 70% of swirl velocity and destabilization force under both FA and PA. Also it was found that CFD analysis could predict the effect of PA and SB on swirl velocity and seal fluid force. For predicting the effect of SB under FA, new steady state CFD analysis method applying frozen rotor interface at SB region was proposed.