Issue34

C. Baron Saiz et alii, Frattura ed Integrità Strutturale, 34 (2015) 608-621; DOI: 10.3221/IGF-ESIS.34.67 615 S ETUP OF NUMERICAL ANALYSES he fading test has been numerically simulated through a thermo-mechanical coupled analysis. During all the 14 braking/recovery steps, the temperature does not have enough time to stabilize in the disc and, for this reason, transient thermal analyses have been performed. After the thermal analyses, a structural simulation has been setup considering both thermal loads and braking forces on the discs. The length of every single braking is 7.55 s, whereas the recovery steps are 32 s length, according to the time between a braking and the next one. During the recovery time simulations, convection is the only applied boundary condition. For all the analysed configurations of the rotors, the convective heat transfer coefficients have been estimated basing on the experiential formulas in literature [16,22], considering an environment (air) temperature equal to 20°. To simulate the cumulative effect of repeated braking, every thermal transient analysis has been linked with the previous and next ones. In this way, the solution of i-th step represents the input data for the following step and so on. The blocks diagram of the implemented procedure is presented in Fig. 8. Figure 8: Blocks diagram of the braking/recovery simulations At the end of the 14th braking, a static structural analysis module has been inserted and linked to the last thermal one. To setup the structural analysis, the temperature distribution over the disc at the end of the last thermal analysis and the braking forces on the pads ( pad F ) have been imposed as boundary conditions. Moreover, also a cylindrical constraint has been applied on the hub of the disks. All FEM models have been meshed with hexahedral elements. The mesh of the straight-vanes disc is shown in Fig. 9. Figure 9 : Mesh of the straight-vanes disc. T