Instability of Unbalance Excited Synchronous Forward Whirl at Rotor‐Stator‐Contact

Abstract

Normally rotor unbalance causes synchronous forward whirl of rotor‐stator systems, even if rub occurs due to rotorstatorcontact. This synchronous forward whirl has to be stable in order to avoid destructive self‐excited dry friction backward whirl, chaotic motions or sub‐ and superharmonic vibrations. However, friction between rotor and stator can cause the synchronous forward whirl to become unstable within certain rotor speed ranges. In the present paper the stability of the synchronous forward whirl caused by unbalance is investigated for rotor motions under contact with the stator. To analyse the stability of synchronous forward whirl the equations of motion are linearised around the stationary synchronous motion. The characteristic polynomial of the perturbations is calculated and the stability is checked by the Hurwitz criterion.

Relevance of the weak equivalence principle and experiments to test it: Lessons from the past and improvements expected in space

“…In GG the time constant for the whirl growth of each test mass is almost 10 days, whirl damping (performed with capacitors as on ground) requires very weak forces and it is off during science data taking, thus leaving the test masses totally passive, as advocated by Braginsky (Table I, entry X). On ground, only rotors with high rotor/stator and bearings noise, or very high dissipation have reported chaotic behaviour [75][76][77].…”

Light and short arc rubs in rotating machines: Experimental tests and modelling

“…A similar topic is studied by Muszyńska [28]. Also Ehehalt and Markert [29][30] [31] study the stability thresholds by means of a Jeffcott rotor. Cole and Keogh [32] use a Jeffcott rotor model to analyse the stability of the rotor-to-stator contact of a test rig.…”

Nonlinear resonances and self-excited oscillations of a rotor caused by radial clearance and collision

“…Recently, Ehehalt [3], Ehehalt et al [4], and Muszynska [5] analyzed orbit patterns of a synchronous forward whirl, subharmonic resonances, and chaotic motions caused by contact and rubbing. Li and Paidoussis [6] showed numerically that self-excited oscillations of a forward and backward whirling modes occur due to rubbing and collisions when a rotating disk flies in a cylinder colliding to its inner surfaces.…”