Experimental Study On Rotordynamic Performance Of A Rotor Supported By Tilting Pad Porous Bearing

With the development of the technologies of aerospace,precision processing,energy & power industry,environment protection and other fields,the requirements of high speed,high efficiency and high precision for rotating machinery,especially for turbo-machinery,are becoming more and more urgent.Gas bearings are an attractive means of support for high-speed rotating machinery due to their low power loss,wide operating temperature range,low viscosity and simple structure.A new type of gas bearing,tilting pad porous bearing(TPPB)which composed of multiple tilting pads utilizes a porous material for throttling externally pressurized gas.Using porous material as restrictor makes TPPB have high stiffness,high damping and high load capacity.The structure of tilting pad can reduce the cross-coupling stiffness when TPPB in operation and improves TPPB’s stability.Hence,TPPB has great potential applied in the field of high-speed rotating machinery.Nevertheless,the majority of the study at present on porous type gas bearing focuses on the numerical analysis of the performance of cylindrical porous journal bearings,there are few researches on the performance of TPPB.Therefore,in this work an experiment rig was modified,TPPBs were used to support a rotor which rotated at high speed,a data acquisition system was established to monitor the lateral vibration of the high-speed rotating rotor,also a data analysis system was set up,analysis of the rotordynamic performance of the bearingrotor system was presented.In this paper,the main work and results are presented in the following aspects:The spherical seat tilting pad porous bearings(SS-TPPBs)were used to support a rotor,and comprehensive experiments were conducted.The influence of different air supply mode,various air supply pressure and different imbalance of the rotor on the rotordynamic response of the bearing-rotor system were studied,the permeability of the porous pads were also investigated.The experimental results demonstrate that when the clearance of the bearing is large,the increase in the air supply pressure into the load-pads of the SS-TPPBs will result in a decrease of the damping of the bearing-rotor system,thus the amplitude of the synchronous resonance of the rotor increases.While the synchronous resonance amplitude of the rotor may decrease to a certain extent as the air supply pressure into the preload-pads of the SS-TPPBs increases.The imbalance of the rotor has a great influence on the response of the bearing-rotor system,and its influence on the synchronous vibration of the rotor is not completely linear.In this paper,the deformation of a Corner-filleted flexure hinge was analyzed based on the small deformation theory of the cantilever beam.The influence of structure parameters on the compliance of the flexure hinge was discussed,and the conclusion that the minimum thickness of the flexure hinge has the greatest influence on the compliance of the flexure hinge was obtained.A flexure pivot tilting pad porous bearing(FP-TPPB)was put forward and designed.Finite element simulation analysis of the compliance of the flexure hinge structure of FP-TPPB was conducted,and the results agree well with the numerical results.The stress simulation analysis shows that the bearing satisfies the requirement of strength.Comprehensive experiments with the rotor supported by FP-TPPBs were carried out.The synchronous rotor response due to a typical split resonance was observed that reveals the anisotropic spring stiffness of the FP-TPPB-rotor system.It is found that the decrease of bearing clearance in the vertical directions will increase the critical speed of rotor synchronous resonance.Experiments using FP-TPPBs with various thickness of the flexure hinge to support the rotor illustrate that the radial stiffness and rotational stiffness of the tilting pad matched with the rotor are the key to the stability of the system.