Rotor/Seal Experimental and Analytical Study on Full Annular Rub

Abstract

Rotor/seal full annular rub, including synchronous (forward) and reverse (backward) precessions, has been investigated both experimentally and analytically. Of particular interest is the finding of reverse precessional full annular rub (dry whip) that occurs repeatedly in small clearance cases without any outside disturbance. The experimental results include rub triggering mechanism, mass unbalance, and rotative speed effects. A simplified mathematical model is used to interpret experimental results. Nonlinear solutions for both synchronous and reverse precessions are obtained along with instability zones. Mass unbalance effect on shifting from synchronous response to reverse rub and destabilizing factors such as dry friction, rotor damping, and seal stiffness, are discussed.

Determination of the global responses characteristics of a piecewise smooth dynamical system with contact

“…Since the synchronous full annular rub bifurcates into the partial rub through Hopf bifurcation, the Hopf bifurcation condition of synchronous full annular rub solution will serve as the boundary between the synchronous full annular rub and the partial rub. As observed in experiment [3,14] and simulations [4], the partial rub ceases to exist after the dry friction backward whirl was triggered by the imbalance with the increase rotating speed. In [17] the physical reason for the onset of dry friction backward whirl was exploited.…”

“…However, it was reported that when an additional outside disturbance (hitting on the shaft) was applied on the rotor during the process, even at a very low rotor speed, the dry friction backward whirl with super-synchronous whirl frequency would be triggered from a synchronous response. A quite different response scenario with the increase of the rotor speed was observed in the tests of [3,16] as: no-rub motion → a synchronous full annular rub → a partial rub → dry whip (heavy rub). So dry whip was triggered solely by the mass unbalance for the rotor/stator systems in this case, which is different from the case mentioned above where an outside disturbance was needed.…”

“…Some papers studied the possible rubbing responses induced through the rotor/stator rubbing and tried to derive the relationship between the rubbing responses and the system parameters, as summarized in [1]. Through the numerical and experimental studies, many rubbing behavior in rotor/stator contact systems have now become well known, for instance, the jump phenomenon and the synchronous full annular rubs [2][3][4], the partial rubs in sub-and super-synchronous whirl [5][6][7], the partial rubs in quasi-periodic whirl [8,9], the chaotic motion [10,11] as well as the dry friction backward whirl which includes two regimes: of dry whirl and dry whip [15][16][17][18].…”

Bifurcation analysis on full annular rub of a nonlinear rotor system

“…Analytical, numerical methods and experiments were employed to investigate the possible contact responses induced by rubbing and derive the relationship between the contact responses and the parameters of rotor systems. Dynamics of full annular rub including synchronous and reverse dry whip were investigated by Yu and Muszynska [7,8] experimentally and analytically. The response and stability for both two cases were obtained, and the effect of parameters, such as mass unbalance, dry friction, rotor damping, and seal stiffness, on shifting from synchronous response to reverse rub were discussed.…”

The mechanism of stiffness increase phenomenon of a rubbing disk

“…This phenomenon seems to be that the stiffness of the rotor system is increased. The rubbing sometimes leads to a machine catastrophic failure [1,2]. It is necessary to understand the mechanism of the sustained rubs for suppressing or controlling the harmful rubs.…”