The increasing market demand for operational flexibility has highlighted the importance of gas turbines optimized for fast transient load variations. Dynamics is a key element in achieving these requirements.

The advanced FE modeling techniques used by ALSTOM for dynamic simulations of the GT (including rotor, bearings and structural parts) have been taken further by the detailed validation of the models used.

The validation exercise involved cold testing with impact hammer and shaker of individual parts and sub-assemblies at the ALSTOM Power Plant in Switzerland.

The influence of operational conditions has been investigated by warm testing, operating the engine with imbalance weights. Important eigenmodes / displaced shapes have been identified during the validation phases and compared with predicted mode shapes. For defined modes, the understanding is increased with particular reference to their excitability.

On the analytical side, key parameters, which affect the dynamic behavior, have been identified by using a detailed systematic approach. Factors affecting individual parts, sub-assemblies and final GT assembly are examined, physically understood and adjusted accordingly. Thus the accuracy of the prediction has been improved in both structural dynamic and rotordynamic assessments.

Furthermore, the guidelines defined for these parameters have been applied to the dynamic calculation for design modifications, successfully introduced on medium sized heavy duty gas turbines for service retrofit. Finally the validation exercise has enabled ALSTOM to improve the understanding of vibration data from engines in the field.

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