Research On The Dynamical Characteristics Of Counter-rotating Dual-rotor System

The counter-rotating dual-rotor system is applied in some aero-engines, and it can decrease the influence of the gyroscopic moments created by the high pressure rotor and the low pressure rotor, reduce the torque of cases, and improve the flexibility of airplanes. So the research on the dynamical characteristics of the dual-rotor system is essential in order to meet the development of the high-performance aero-engines. Two kinds of dual-rotor systems, which have different inter-shaft connecting structures, are studied. In one of the dual-rotor systems, the low pressure rotor is mounted on the inter-shaft bearing's inner ring and the high pressure rotor is mounted on the inter-shaft bearing's outer ring. In the other, the low pressure rotor is mounted on the inter-shaft bearing's outer ring and the high pressure rotor is mounted on the inter-shaft bearing's inner ring. The main contents of this paper are as follows.(1) The direct transfer matrix method is developed, and the dynamical model of the dual-rotor system is set up. Using the model, the critical speed characteristics are studied, and the distributions of the system's strain energy and the influences of the supporter's stiffness, the speed ratio and the gyroscopic moments to the critical speeds are analyzed. Then the critical speed characteristics of two kinds of dual-rotor systems are compared. Furthermore, the experiments results on the influences of the supporter's rigidity to the critical speeds are given, and the laws from the calculation results are the same as those from the experiment results. It is found that, the gyroscopic moments is the primary reason of the difference between the critical speed characteristics of the dual-rotor systems which have different rotating directions.(2) The steady-state response of dual-rotor systems is studied by the direct transfer matrix method. The orbit and location of the centroids of dual-rotor disks are analyzed, and the calculational conclusions are validated by the experiments. It is found that, when the dual-rotor system passes the critical speed, the disk centroid location excited by itself will turn about 180 degrees, but another rotor won't.(3) Considering the effect of the varying compliance vibration of the inter-shaft bearing, the non-linear changing rule of the inter-shaft bearing stiffness is analyzed when the bearing co-rotates and counter-rotates. Based on the analyses of motion and load relations, the analytic model of the inter-shaft bearing's dynamical characteristics is set up. The roller spinning speed, the cage speed and the load of rollers are analyzed, and the performances of theinter-shaft bearings are compared, when the bearing operating in different working conditions. The conclusion indicates that, the counter-rotating inter-shaft bearing has more loaded rollers, lower slip ratio, but it has higher roller spinning speeds, so each of the inter-shaft bearings for two rotating directions possesses the respective advantage.(4) Considering the non-linear stiffness of inter-shaft bearings, the dynamical equation for the non-linear vibration analysis of the counter-rotating dual-rotor systems is given. The influences of the rotor speeds, the amount of unbalance, and the radial clearance of inter-shaft bearings to the system response characteristics are studied. It is found that, the non-linear vibration can be reduced by selecting the parameters, including the rotor speed and the amount of unbalance. The non-periodic vibration can be avoided by decreasing the radial clearance of inter-shaft bearings.In conclusion, the critical speed characteristics, the steady-state response, the dynamical characteristics of inter-shaft bearings and the non-linear vibration response of the counter-rotating dual-rotor systems are studied in this paper. The results can provide the theoretical direction for the design and the operation of dual-rotor system, and it is helpful to gain higher dynamical characteristics of the dual-rotor sytems of aero-engines, so the contribution possesses an important theoretical significance and application value in engineering.