Examination of the dynamic properties of 1st stage rotor blades in one - pass engine compressors under operating conditions

This article includes studies of vibration and stress amplitudes in the Is' stage rotor blades of jet trainer one-pass engine compressors before and after refurbishment in operating conditions. The presented results were obtained using SAD-2 blade vibration amplitude registering and measuring apparatus. The same tests were carried on the same one-pass engine after modernisation. Example oscillograms from the vibration tests of the 16 blades are shown in this article, where show the vibrations of three randomly selected one-pass engines after refurbishment (marked 1, 2 and 3) out of a total of 50 engines. The engine vibration spectra cover the full rotation speed range. The difference between the vibration amplitudes of 1st stage rotor blades, in one-pass engine compressors before and after the refurbishment, is results from the difference in how the blades were attached to the disc. Before modernisation the hammer-type root was used, whereas after refurbishment dovetail-type fittings were applied. Furthermore, it was confirmed that there is nocoupling via the blade disc occurred when the blades were arranged on the disc according to the sinusoidal order of their free vibration frequencies. In such cases recorded vibration amplitudes remain within the average range (from 100 to 120 MPa in terms of stress).