Rotor-to-Stator Friction Simulation with Nonconstant Stiffness of the Contact Surfaces and Small Clearance between Them

Analytical and numerical modeling approaches for the contact-working system of turbo- and electric machines have been developed. The simulation allows determining some dynamic characteristics and loads in the rotor–stator system when there is a loss in clearance between them and there occurs subsequent motions with impacts or without separation from each other. In the system, the rotor and stator are deformable, the stiffness of rubbing surfaces is variable, and the working clearance between them is extremely small (50–500 times less than the rotor radius at the contact point). It is shown that the effect of the absolute elasticity for stator generates a significant change in natural oscillations of the coupled rotor–stator system, that is, a significant change in its eigenfrequencies and eigenmodes. It is noted that the elastic deformation of rubbing surfaces leads to a nonlinear increase in their contact stiffness, which consists of quasi-static and dynamic components. The consequences of an extremely small clearance are an elastic deformation of the contact surfaces commensurate with it (up to half the clearance size at the point of contact) during whirling with slipping of rotor over stator, as well as the disappearance of pure rolling, which is accompanied by the actual absence of rotary speeds even at low frequencies of contact whirling. The resulting diagrams of changes in the contact stiffness and whirling frequencies and the XY trajectories can serve as sources of initial information for identifying the operation of a real rotary machine on the threshold of a dangerous whirling with slipping and whipping and for further studies of contact oscillations of rotors.