The energy industry depends on centrifugal compressors to produce, process, re-inject and transport many different gases. Centrifugal compressors use one or more impellers to impart momentum to the flowing gas and, thereby, produce an increase in pressure through diffusion. As the operating pressure in a compressor increases, the fluid-rotor interaction at the seals and impellers become more important. Also, the new generation of mega-scale Liquefied Natural Gas (LNG) compressors is dependent on accurate assessment of these forces. The aerodynamic forces and cross-coupled stiffness from the impellers cannot be accurately predicted with traditional methods and must be estimated with semi-empirical formulations. The result of these inaccuracies is a potential for compressor designs that can experience unexpected, dangerous, and damaging instabilities and subsynchronous vibrations. The current investigation is intended to advance the state-of-the-art to achieve an improved, physics-based method of predicted aerodynamic destabilizing cross-coupling forces on centrifugal compressor impellers using Computational Fluid Dynamics (CFD). CFD was employed in this study to predict the impeller-fluid interaction forces, which gives rise to the aerodynamic cross-coupling. The procedure utilized in this study was developed by Moore and Palazzolo [10], which applied the method to liquid pump impellers. Their results showed good correlation to test data. Unfortunately, no such data exists for centrifugal compressors. Therefore, in order to validate the present model, comparisons will be made to predict the instability of an industrial centrifugal compressor. A parametric CFD study is then presented leading to a new analytical expression for predicting the cross-coupled stiffness for centrifugal impellers.

This content is only available via PDF.
You do not currently have access to this content.