Contact Status Analysis of Rod-Fastened Rotors With Hirth Coupling in Gas Turbines

Abstract

The aim of this paper is to provide some basis for the design and assembly of a rod-fastened rotor with Hirth coupling. The rod-fastened rotor is comprised of a series of discs clamped together by a central tie rod or several tie rods on the pitch circle diameter. The key difference between a rod-fastened rotor and an integrated one is the existence of contact interfaces. The contact status of contact interface in the rod-fastened rotor is the key concern for accurate rotor dynamic analysis. Therefore, the method of accurately describing the slippage status and contact status is presented in this paper. The approach of eliminating the slippage and making the radial contact pressure distribution more uniform is also presented. According to the characteristics of Hirth coupling, one model of a turbine end rotor with Hirth coupling of a heavy duty gas turbine was built. The three-dimensional finite element contact method and non-linear behaviors such as friction were also taken into account. The effect of pre-tightening forces, centrifugal forces and overhung rim lengths on the radial slippage including initial radial slippage usi and dynamic radial slippage usd of contact interface was determined. A dimensionless coefficient cr was also defined to describe the radial contact pressure distribution of contact interface which was influenced by the values of pre-tightening forces, centrifugal forces and wheel rim lengths respectively. The results of Hirth coupling indicate that the initial radial slippage increases with the pre-tightening forces, and for a fixed pre-tightening force, usi decreased with the increase of overhung rim length. In addition, there is an optimum rim length to eliminate the dynamic radial slippage usd produced by the change of the centrifugal force. Through the analysis of contact pressure distribution, we know that the reasonable design of the load relief trough processed in the overhung rim makes the contact pressure distribution more uniform. Finally, the effect of temperature load on the radial slippage and contact pressure distribution was investigated.