On-line calculation methods are currently used to evaluate stress and temperature of engine components in order to assess fatigue damage accumulation and residual life. On-line temperature calculation algorithms are necessary because temperature affects fatigue damage curves. Since it is neither possible nor necessary to compute on-line temperature on the whole component, a number of critical nodes are selected and their temperatures are evaluated with simplified algorithms. A well-known technique used to reduce the degrees of freedom of dynamic structural FE models is the component modes synthesis (CMS). By this technique the nodal degrees of freedom are divided into two sets: active and omitted. Active degrees of freedom are translated into the reduced model, while omitted ones are replaced by the most important modal shapes, in order to evaluate the dynamic behavior of the system. In the present work CMS has been applied to thermal transient analyses, in order to compute temperatures in low-pressure turbine discs critical areas. Due to the complexity of the geometry, the disc has been sub-structured into super-elements. The methodology has been tested on axi-symmetric FE model of a low-pressure turbine disc, comparing thermal transients performed by complete FE model with those evaluated by the sub-structured model.

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