Unbalance response and critical speed analysis of a flexible gas turbine rotor supported with foil bearings

The analysis of rotor dynamic aspects of a gas turbine is very much essential before the start of manufacturing. For better accuracy often designers look for 3D representations of the rotor models, however, these models have its advantages as well as disadvantages. The major disadvantages are the model size increases significantly. However, this issue can be addressed by model reduction techniques such as the use of external superelement (SE) which is obtained by component mode synthesis (CMS) or similar approaches for model reduction. The major limitation of this technique is that: Analysis needs a detailed 3D CAD model before the start of analysis. So, when we do not have the detailed 3D models of compressors and turbines or we want to study the effect of many design modifications on the performance of a rotor shaft system, while keeping the complexity low an equivalent mass representation for turbine and compressor systems are very useful. In this paper we have used an equivalent mass representation of a small gas turbine rotor and studied different performance performances like stability, unbalance response and modal frequencies while using different values for support systems of a rotor shaft system. Using parametric study, we could successfully propose the design modification for changing peak amplitudes as well as natural frequencies of the rotor dynamic system supported with a foil bearing.