Dynamic Characteristics of Rod-fastened Rotors based on Persson Contact Theory

Abstract

The rod-fastened rotor (RFR) is comprised of a series of discs clamped together by several rods on the pitch circle diameter. Most researchers have studied the contact stiffness of rod-fastened rotor by using Hertz contact theory. That is: the contact layer of the disc consists of a great number of asperities and every asperity is approximated as a bump. However, as the contact angles of the asperity exceed 30°, the result would be not accurate if Hertz contact theory is applied. And the contact angles of asperities which exceed 30° are so common in real contact. Besides, it is not consistent with the actual situation that the real contact layer is approximated as several spherical bumps with equal radius of curvature against a rigid flat. Hertz contact theory can be valid only with the condition that the real contact area is much smaller compared to the nominal contact area. So we build a more accurate contact model based on Persson contact theory. Dynamic characteristics of the contact layer are analyzed and differences between this two contact theory are presented. We calculate the critical speed and the unbalance mass response based on Riccati transfer matrix method when the rotor is rigid supported or supported by circular journal bearings or tilting pad journal bearings. The influence of pretightening forces on the critical speed and the unbalance response are exposed in this paper and their corresponding mode shapes are shown. The relationships of the critical speed and the vibration response of the rod fastened rotor with different pretightening forces are also given.