Abstract
A rotor–stator model of a turbogenerator is introduced in order to investigate speed transients with rotor-to-stator rubbing caused by an accidental blade-off imbalance. In order to assess the angular deceleration of the rotor due to rubbing, the angular position of its cross-section is considered as an unknown of the problem. Displacement fields are discretized through a finite element formulation. The highly nonlinear equations due to contact conditions are solved through an explicit prediction–correction time-marching procedure combined with the Lagrange multiplier approach dealing with a node-to-line contact strategy. The developed numerical tool is suitable for analyzing rotor–stator interactions in turbomachines as the system passes through critical speeds during an accidental shutdown. The sensitivity of the system response to modeling, physical and numerical parameters is investigated. The results highlight the significant role of the friction coefficient together with the diaphragm modeling, from rigid to fully flexible, in the interaction phenomenon. Rigid models have the advantage of simplicity and provide reasonable estimations of the overall response of the turbine. A flexible model, however, may be more computationally intensive but is more appropriate in order to accurately capture quantities of interest such as shaft eccentricity and bearing loads.
Highlights
In nuclear power plant turbosets similar to the one pictured in figure 1, the reference design–basis accident consists of a blade–off in the last stage of the low pressure turbine
A rotor–stator model of a turbogenerator is introduced in order to investigate speed transients with rotor–to–stator rubbing caused by an accidental blade–off imbalance
In order to assess the angular deceleration of the rotor due to rubbing, the angular position of its cross–section is considered as an unknown of the problem
Summary
Known to be a serious malfunction in turbomachinery, has been the subject of a large amount of research and a detailed overview is provided in [25, 23]. First mathematical models dedicated to rubbing issues were as simple as Jeffcott rotors [28] They were extended to flexible rotors through finite element approaches and/or modal synthesis techniques [15] allowing for more realistic descriptions. Two main families are usually found in the literature: implicit versus explicit formulations [26, 27] It is observed in [14] that the results highly depend on Newmark parameters for problems involving strong nonlinear terms such as direct contact constraints. The prediction– correction algorithm forward increment Lagrange method developed in [32] embeds the Lagrange multiplier approach in an explicit technique keeping the advantages of both It has been proved reliable for contact–impact problems [1] by properly satisfying contact detection and ensuring displacement compatibility and is preferred in this study
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
