Engineering MECHANICS, Vol. 17, 2010, No. 3/4, p. 269–279 269 THE INFLUENCE OF CONTROLLED BUSHING MOVEMENT ON BEHAVIOUR OF A ROTOR IN SLIDING BEARINGS Jiˇ r´ ı T˚ uma*, Jiˇ r´ ı ˇ Simek**, Jarom´ ır ˇ Skuta*, Radim Kleˇ cka* Test stand for investigation of the influence of bearing bushing movement control on behaviour of a rigid rotor supported in sliding journal bearings was designed. The stand was equipped with two pairs of piezoactuators, enabling to move each bearing bushing in two directions, and with two pairs of relative sensors tracing shaft move- ment at both bearings. The initial tests showed quite unexpected phenomena, which should be cleared up, before experiments with controlled bearing bushing movement could be started. Finally the system began to operate according to predictions and it was possible to start intended experiments. Some results of the rotor behaviour with and without piezoactuator action are presented. Keywords : test stand, hydrodynamic journal bearings, rigid rotor, controlled bush- ing movement, piezoactuator, relative sensor, oil whirl instability, elastic support 1. Introduction Rotor instability is one of the most serious problems of high-speed rotors supported in sliding bearings. With constantly increasing parameters of new machines problems with rotor instability are encountered more and more often. To study possibilities of affecting rotor behaviour by controlled movement of bearing bushings, test stand was designed, ma- nufactured and assembled in the scope of Czech Science Foundation grant project, which was inspired by work [3]. Test stand located at Technical university of Ostrava showed some features, which were quite unexpected in such a simple system. The reasons of this unorthodox behaviour had to be found before experiments with bearing bushing excitation could be started. 2. Test stand design As can be seen in Fig. 1, test stand [1] consists of a rigid shaft 7 supported in two cylin- drical hydrodynamic journal bearings. Bearing bushings are supported in rubber ‘O’ rings, which ensure sealing of oil inlet and at the same time enable movement of bushings within the clearance in bearing casing. Bearing bushings can be excited by means of piezoactua- tors 12 oriented in vertical and horizontal directions and fasted to the frames 13 and 14 . The test shaft is driven by high-frequency motor 3 through elastic coupling 6 , constituting two joints, so that the shaft is decoupled from motor and free to move. Shaft movement is ob- * prof. Ing. J. T˚ uma, CSc., Ing. J. ˇ Skuta, Ph.D., Ing. R. Kleˇ cka, Ph.D., V ˇ Sb´aˇ nsk´a, TU Ostrava, tˇ r. 17. listo- padu, 708 33 Ostrava ** Ing. J. ˇ Simek,CSc, TECHLAB s.r.o., Sokolovsk´a 207, 190 00 Praha 9