Frequency Estimation of Backward-Whirl During Rotor-stator Contact

Benjamin Siegl¹; Oliver Alber¹; Richard Markert¹

¹ Institute of Structural Dynamics, TU Darmstadt

doi:10.20906/CPS/COB-2015-2702

Resumo

This paper deals with an analytical estimation for the negative frequency components which can be detected during rotor-stator contact for a motion pattern called backward-whirl. If this backward-whirl occurs depends on the parameter set of the rotor, stator and contact area. But if it takes place usually the amplitudes become very high and severe damage might be caused to the system. As a conclusion this motion pattern should be avoided during operation. The presented method is based on previous research which estimated the backward-whirl frequency of a Laval rotor in contact with a stator with one degree of freedom. This paper extends this method for rotors with multi-degrees of freedom (MDOF) contacting MDOF stators. A phenomenon which is characteristic for such systems is the transition from a backward-whirl motion pattern to another one with potentially even higher amplitudes. Typically, the gap between rotor and stator is very small compared to the backward-whirl amplitudes. Because of this, the negative backward-whirl frequency component for each chosen rotor speed is very close to a negative natural frequency of the coupled rotor-stator system. Thus, this coupled natural frequency can be used for a bi-frequent approach to solve the equations of motion. This gives rise to the calculation of the resulting backward-whirl amplitudes for a MDOF rotor at each rotor speed.

Palavras-chave: Rotor dynamics; Rotor-stator contact; Backward-Whirl