Influence of Leak Path Friction on Labyrinth Seal Inlet Swirl

Abstract

Labyrinth seals in various kinds of rotating machinery often generate driving force components that may increase the unstable vibration of the rotor. The evaluation of labyrinth seal forces has been documented by CFD analysis but the leak path geometry influence on the resulting entry and reverse pumping flow prior to the labyrinth seal geometry has only recently been studied in detail. The labyrinth seal driving forces are known to increase with an increase of the inlet swirl velocity ratio. In a previous work, a commercial CFD program was used to simulate leak path and labyrinth seal flows of various centrifugal compressor eye seal leak flow geometries. For each case, 3D models with an eccentric rotor were solved to obtain the leakage flow, velocity vector, chamber pressure, and the average chamber swirl entering the seal. The current article will present the bulk flow analysis predicted entry swirl ratio for the same geometries and sealing conditions. The influence of the effective disk friction will be considered in the calculation of the bulk flow results by using modified turbulence factors. The CFD simulation showed that the inlet geometry and the resultant reverse pumping flow in the entry channel can have a significant influence on the calculated chamber average swirl velocity ratio. Generally, the bulk flow analysis gives a pessimistic estimate of the swirl velocities as compared to the CFD calculations.

KEY WORDS:

• Labyrinth
• Seals
• Leakage
• Stability
• Rotordynamics

Review led by Jim Netzel