EFFECT OF GAS FLOW IN IMPELLER-HOUSING GAPS OF CENTRIFUGAL COMPRESSOR STAGE ON EFFICIENCY AND AXI-AL FORCE

When operating powerful centrifugal compressors, in particular, pipeline compressors, some modes of operation pose problems with the thrust bearing capacity. Back in 1970, the senior of the authors carried out a numerical study of the effect of flow rotation in the housing–impeller gaps. It was shown that in the impeller–shroud gap the flow rotates faster than in the gap near the main disk. The reason is that the leakage flow of the labyrinth seal of the shroud enters this gap. The flow introduces the rotation created by the impeller blades. The authors made a compu-tational CFD study of the effect of friction stress in the housing–shroud gap on the thrust force and efficiency of the centrifugal stage. Calculations of a stage with an impeller diameter of 409 mm are made with a hydraulically smooth housing wall in the gap near the shroud at rough-ness of 0.25, 05, 0.75, 1.0, 1.5 mm. With a roughness of 0.25 mm, the axial force decreased by 21% at the cost of reducing the efficiency by 0.5% for a stage with a flow coefficient Φ = 0.0492. With a roughness of 1.5 mm, the efficiency decreased by 0.9%, and the axial force de-creased by 32.6%. In exceptional cases and as a temporary measure to decrease the thrust force, it is possible to use deceleration of the flow in the gap at the shroud disk. A special calculation showed the role of leakage in the labyrinth seal. With a hermetic labyrinth seal, the efficiency would be higher by 0.9%, the loading factor would be higher by 0.8%, and the axial force would be less by 22.8%. The calculation also showed that during corrosion of the housing walls within both gaps, friction losses on the surfaces slow down the flow rotation in both gaps, reduce the efficiency, but have practically no impact on the thrust force.