A Comparison Study on Co- and Counterrotating Dual-Rotor System with Squeeze Film Dampers and Intermediate Bearing

Abstract

Nonlinear dynamic model of a coaxial rotor system was established with a method combining the finite element method and the fixed interface modal synthesis method. Then an implicit time domain method was presented to solve the nonlinear equations of motion; thus dynamic characteristics of the rotor system can be obtained. With nonlinear forces of squeeze film damper and intermediate bearing considered, nonlinear dynamic response characteristics of the co-and counterrotating coaxial rotor system under multiple unbalance forces were studied and compared in this work. It was found that the critical speeds of the corotating system were equal to or slightly higher than those of the counterrotating case due to the gyroscopic moments. The results showed that the unbalance excitation frequencies are dominant in the responses of the rotor system. Besides, due to coupling effect of the intermediate bearing some combinations of the unbalance excitation frequencies were also observed in the spectrogram but the combinations were different for co-and counterrotating cases. Stability and periodicity of the rotor system were investigated with bifurcation diagram, Poincare map, and phase diagram. It was found that the rotor system executes four-period quasi-periodic motion around critical speeds.

Research nonlinear vibrations of a dual-rotor system with nonlinear restoring forces

“…Free vibrations in the dual-rotor system with no external force and no damping are governed by the following equations, which are given by putting e 1 = e 2 = 0, τ = 0, c 11 = c 12 = c 21 = c 22 = 0 into Eqs. (16) and (17).…”

“…(39) in Eqs. (16) and (17), and the rotating relationship is set as ω 1 t = -ω 2 t = 2nπ (n represents the number of cycles in the system response) to eliminate time (39) x 1 = P L cos 1 t + L , x = P cos 1 t + , x 2 = P H cos 2 t + H y 1 = P L sin 1 t + L , y = P sin 1 t + , y 2 = P H sin 2 t + H parameter t in the system. The six-element nonlinear equations can be obtained as follows:…”

“…Leading the nonlinear coefficient β (0) to Eqs. (16) and (17), the dynamic characteristics of the dual-rotor system are studied with influences of the coefficient β (0) . Both cases of α = 2 and α = 1.8 are discussed.…”

“…Considering the nonlinear coefficients β (0) and ε (1) , Eqs. (16) and (17) are solved and we discussed influences of the nonlinear coefficients β (0) and ε (1) on the dual-rotor system.…”

“…Deng et al [14,15] proposed mathematical model to formulate nonlinear displacements, elastic deformations and contact forces of bearings of the dual-rotor system, and systematically analyzed the dynamic characteristics of the dual-rotor system about influences of rotational speeds, clearance of the inter-shaft bearing, the number of rollers and geometry parameters of bearings. Luo et al [16,17] established a high-dimensional nonlinear dynamic model of a dual-rotor system by using the finite element software and fixed the interface modal synthesis method. They considered nonlinear forces of a squeeze film damper and the intershaft bearing and studied the nonlinear dynamic response characteristics of the counter-rotating dual-rotor system with varied unbalance forces.…”