Experimental and Theoretical Study on Swirl Braked Labyrrinth Seal

Abstract

The objects of this study are to present new gas seals, which have several control fins at a groove part of straight labyrinth seal, and to evaluate the dynamic characteristics of the seals experimentally and theoretically. The new seals are expected to reduce the tangential velocity and to control the instability of the rotor system. The experimental test results are presented for eight multiple-pocket grooved gas seals with different number of control fins and stages to put control fins. In the theoretical study, seal chamber is divided into two control volumes. Then, the equations are formulated for each control volumes. The fluid forces acting on the rotor are obtained. For the circumferential velocity, the groove part is divided into three control volumes then the decrease in circumferential velocity by the effect of the control fins is evaluated at each control volume. Then, the circumferential velocity and dynamic fluid force were measured for 8 types of seals which were changed the number of fins and location of the fins in the experiment. In the theoretical analysis the flow equation which suppress the circumferential velocity was taken into account in the conventional labyrinth seal equation and solved numerically. From the above experimental and theoretical investigations, the followings are concluded that control fin installed in the grooves is effective to suppress the circumferential velocity. The effect of the fins is large at the first and second stage from the inlet of a seal. The effect of fins on the stabilization of rotor was large for 8 and 4 fins in the first stage.

Rotordynamics of Turbine Labyrinth Seals with Rotor Axial Shifting

“…Specifically, the low portion immediately downstream of the first rotor block dominates the rotordynamic stability characteristics of the high-low labyrinth. This is compatible with the recent experimental results of Iwatsubo and Iwasaki [17] who found that adding swirl brakes at the inlet, particularly inside the first and second cavities, was effective in dramatically reducing the net destabilizing force as well as the circumferential swirl velocity.…”