Investigation of the Effects of Dimensional Variations and Manufacturing Tolerances on the Modal Behavior of the IGT۲۵ Combustion Chamber

The dynamic behavior of a gas turbine combustion chamber is governed by two main external excitation sources: the dynamic pressure fluctuations generated by combustion instabilities and the unbalanced forces transmitted from the rotor. The vibrations induced in the combustion chamber structure by these excitations may cause structural resonances, which play a crucial role in the analysis and design of the chamber. Such resonant conditions can lead to failure, particularly through the activation of high-cycle fatigue and wear mechanisms, thereby directly or indirectly reducing the structural lifespan of the combustion chamber. Achieving an accurate and reliable dynamic analysis is essential for determining the chamber's modal characteristics, including its natural frequencies and mode shapes, which enable precise identification of the frequency ranges where excitation and structural responses may interact. Various factors—including boundary conditions, geometric configuration, and finite element modeling parameters—significantly influence the predicted modal properties. The IGT۲۵ gas turbine, one of the products of OTC Company, incorporates an annular combustion chamber with complex geometry and multiple assembled components. During the manufacturing and assembly stages, dimensional tolerances are defined within standard acceptable limits; therefore, individual chambers may exhibit slight geometric variations in accordance with these tolerances. In this study, the experimentally obtained natural frequencies, extracted through impact testing, are compared with the numerical modal analysis results. The effects of dimensional variations and manufacturing tolerances of the IGT۲۵ combustion chamber on the modal properties—specifically the natural frequencies and mode shapes—are then investigated. Determining the variation range of the structural natural frequencies due to manufacturing tolerances and assembly-induced dimensional deviations is essential for assessing their potential interaction with excitation frequencies.

کلیدواژه ها:

Modal Analysis ، Impact Hammer Test ، Combustion Chamber ، Gas Turbine