Research On Dynamic Characteristics Of Rotor-casing Systems With Rubbing

The clearance between the blade-tip of rotating component and inner casing is called blade tip-gap,which has become one of important parameters to measure the performance of rotating machinery.Recent years,in order to reduce weight and pursue high thrust-weight ratio,blade tip-gap should be as small as possible,which can lead to the rubbing between the blade tip and inner casing easily.Rubbing in rotating machinery is a common nonlinear dynamic phenomenon,therefore researches dedicated in the effects of rubbing on Iocal/global damage and dynamic characteristics have a great significance.Taking a rotor-casing system as the research object,the numerical model is established based on ANSYS software,and the complicated nonlinear dynamic characteristics of rotor-casing rubbing are studied in this paper.The main contents in this paper are as follows:(1)Using lumped mass points(LMPS)to simulate the disk and casing,the finite element(FE)model of the rotor-casing system is established in ANSYS.In the case of local and global rubbing,the influences of different parameters such as rotational speed,misalignment distance,rubbing stiffness(also known as contact stiffness)on the rubbing induced responses are discussed.The results show that severe rubbing and multi-periodic motion can be observed under the large misalignment distance.In addition,due to the enormous energy of rotor,fractional frequencies and multi-periodic motion can be observed under the high rotational speed.(2)Using shell element which can consider the local deformation effect to simulate the casing,FE model of the rotor-casing system considering the coupling effect between the rotor and the casing is established.In order to improve the computational efficiency,the super-element model of the casing is adopted.The accuracy of super-element model is also verified by comparing the system natural characteristics,rubbing responses obtained from super-element and non-super-element models.In the case of local and global rubbing,the influences of different parameters such as rotational speed,misalignment distance,rubbing stiffness,casing stiffness on the rubbing induced responses are discussed.Because the rubbing can lead to an auxiliary support,which can increase the natural frequency of the system,and this makes the resonance peak backwards under the high rotational speed.For global rubbing,the continuous contact between rotor and stator becomes the intermittent rubbing(i.e.,many times rubbing in every rotational period)with the increase of casing stiffness.(3)Simulating the blades by establishing LMPS at the centroids of the blades,the FE model of the rotor-casing system is established.In the case of local/global rubbing,the influences of different parameters such as rotational speed,misalignment distance,rubbing stiffness on rubbing induced responses are analyzed.The results show that the number of blades experiencing rubbing gradually increases with the increasing rotational speed.Moreover,with the increase of the rubbing stiffness,rubbing force increases,but the number of blades experiencing rubbing remains unchanged.(4)Simulating the blades and the disks by Timoshenko beam element and shell element,respectively,the FE model of the rotor-blade-casing system is established.The accuracy of the presented rubbing model is validated by comparing the test results and FE model results;The responses difference between the two FE models is carried out by comparing the rigid-disk and rigid-blade model and this chapter model.In the case of fixed point rubbing between blade tip and inner casing,the influences of different parameters such as rotational speed,stagger angle,rubbing stiffness on system vibration responses are analyzed.