Abstract
Rotordynamic forces on pump impellers and turbine runners are reviewed. First, it is shown that the rotordynamic instability occurs when the tangential component of the effective rotordynamic force is in the direction of rotor whirl. In many cases of centrifugal impellers, rotordynamic forces can cause forward whirl at supercritical speeds where the rotor is running more than twice the first critical speed. This occurs when the impeller is operating in a volute or a vaned diffuser, or when the clearance between the front shroud and the casing is small. However, when the change of the leakage flow due to displacement is important, the fluid force moment can cause rotor whirl even when the rotor speed is significantly lower than the first critical speed. The instability can be avoided by placing the seal at the exit of the leakage flow or changing the opening/closing convention of the seal associated with the deflection of the rotor.
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Tsujimoto, Y. (2017). Rotordynamics of Turbopumps and Hydroturbines. In: d'Agostino, L., Salvetti, M. (eds) Cavitation Instabilities and Rotordynamic Effects in Turbopumps and Hydroturbines. CISM International Centre for Mechanical Sciences, vol 575. Springer, Cham. https://doi.org/10.1007/978-3-319-49719-8_5
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DOI: https://doi.org/10.1007/978-3-319-49719-8_5
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