Affection of manufacturing errors of a gas turbine shaft on its torsional oscillations


Аuthors

Usmanov A. R.

Peter the Great St. Petersburg Polytechnic University, 29, Polytechnicheskaya str., St. Petersburg, 195251, Russia

e-mail: ysman2d@gmail.com

Abstract

In this work the affection of the shaft manufacturing errors on its torsional oscillations was analyzed. In the literature review part the author considered the cases, on which imperfection in shafts could lead to effects, which could be hazardous for the engine during its operation. For instance, if there is imperfection in a shaft, there could occur an unbalance during its operation, which could lead to additional deflection of the shaft. Such effects prove the necessity of the proper controlling of gas turbine part size deviation (tolerances), which could be conducted with mathematical modelling methods applied. In the present work the analysis of torsional oscillations of the considered rotor was carried out by implementing the finite element method. The finite element model of the rotor was constructed and the first torsional natural mode and the corresponding first natural frequency of the rotor were obtained. The comparison of the obtained results with the ones of the calculation with implementation of the simplified analytical approach showed, that the finite element model gives the results close to the analytical one. Then the finite element model was used to estimate the influence of the manufacturing errors of a shaft on its torsional oscillations. For this purpose, in the geometrical model of the shaft being the part of the rotor considered before the specified thickness variation was inserted and the calculation was repeated with the same source data. The results showed, that thickness variation presence leads to the shift of the area of the stress concentration to the zone of the shaft thinning, which matches assumptions. At the same time, the maximum value for the stress raised by 12% (the value for the natural frequency didn’t change). Overall, shaft imperfection presence could significantly affect its stress-strain behavior upon torsional oscillations. In the present work it was also demonstrated, that the shifting of the area of stress concentration caused by the presence of manufacturing errors could lead to the corresponding shifting of the area of potential cracks. Therefore, the developed method can be implemented in order to determine such zones more accurately.

Keywords:

rotor dynamics, manufacturing errors, tolerance, torsional oscillations, shaft

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