Design and Implementation of Swirl Brakes for Enhanced Rotordynamic Stability in an Off-shore Centrifugal Compressor

Abstract

Rotordynamic stability of gas compressors at high speeds and operating pressures is a significant technical challenge. Dynamic instability must be avoided for the sake of safe, reliable and continuous operation of turbomachinery. Experience and literature have shown that one of the main sources of instability is the swirl within the secondary leakage path in shrouded impellers, especially the swirl entering the shroud seals. The technical brief presents the design and implementation of swirl brakes for centrifugal compressors with Teeth-on-Rotor seal configurations for shrouded impellers. Discussion includes (a) aerodynamic design of swirl brakes with the help of Computational Fluid Dynamics (CFD), (b) sub-scale testing of the swirl brake design in an instrumented single-stage test rig to measure the inlet swirl ratio in a shrouded impeller, (c) full-scale prototype shop-testing and qualification, with and without the swirl brakes in a closedloop test facility, and (d) results of incorporating the swirl brakes at an off-shore compressor installation to improve rotordynamic stability.