Influence of labyrinth seals in cavities on the flow of an axial compressor

Abstract

The vortex structure inside the upstream cavity-trench depends on the cavity outlet angle. Independently of the cavity outlet angle, the interaction of the upstream rotor wake and the leakage flow induces a wake-leakage vortex. The proximity of the cavity outlet with the rotor modifies the number of induced wake-leakage vortices. This investigation reveals that in the downstream cavity-trench a windage effect occurs similar to the upstream cavity-trench but with minor intensity. The leakage flow cannot recirculate to the upstream cavity-trench and be reheated. All investigated configurations modify the recovery factor near the hub, namely below 10% span with the inclusion of the cavity. The Kerrebrock and Mikolajczak’s effect remains on the stator suction-side at the hub due to the leakage flow transported by wake-leakage vortices while at mid-span the effect appears on the stator pressure-side. The overall performance of the third compressor’s stage shows that the effect of the cavity outlet angle is more influential at lower leakage rates. As the leakage rate progressively increases, the cavity outlet angle loses its influence. Independently of the cavity outlet angle, the inclusion of the cavity in the third stage reduces the total pressure level and increases the total temperature level of the stage as a consequence of the transport within the wake-leakage vortices. This combination results in a more pronounced deterioration of the isentropic stage efficiency. For every 1% of labyrinth seal clearance increase, the stage total pressure ratio decreases between 0.114 to 0.132%, and total temperature ratio increases between 0.039 to 0.051% resulting in an isentropic efficiency reduction by 0.828 to 0.944%.