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The present works investigates with numerical methods the performance of longitudinal ventilation system and the structural response of a tunnel in case of fire. Computational fluid dynamics allows to simulate the flow field in a generic domain solving the equations of Navier Stokes. Several codes have been developed for the purpose and due to its specific development the code Fire Dynamic Simulator has been chosen, FDS. FDS is used to evaluate the flow field induced by a fire and by jet fans in order to evaluate the capability of the devices to confine the smoke. Jet fans in tunnel have been modelled and validated against different experiments in cold flow, in order to compare pressure and velocities. The fire has been later added and an entire tunnel has been simulated with jet fan activated, the results have been compared with experimental measurements for temperatures, velocities and volume flows. The simulations assessed the capabitity of FDS to simulate jet fans and fire predicting the pressure rise, velocity decay of the jet and the smoke confinement. FDS is also capable to correctly predict the throttling effect inside a tunnel considering the reduction of the volume flow rate across the tunnel due to the fire. FDS has been later used also to predict the thermal loads on a concrete structure exposed to fire. A structural code developed at the University of Padua, Comes-HTC, has been used to simulate the response of concrete at high temperature. The code has been coupled with FDS in order to use a realistic set of boundary conditions for the structural calculation. To couple the two codes an interpolation approach has been proposed and verified for the interfacing of Cartesian grids and structured grids. The coupled approach has been applied to study a concrete slab exposed to different fire scenarios, evaluating the influence of the fire growth rate and the HRR per unit of area. The coupled analysis has been applied to study a rail coach on fire in a tunnel, the study focused both on the modelling of the fire scenario and on the response of the vault. The coupled approach has been developed to transfer the results from FDS to Comes-HTC, however in order to study the influence of the structure on the fluid a two way coupling has been tested for the slab exposed to fire. Another coupled approach has been proposed embedding the Comes-HTC model in FDS. The different approaches showed similar results, therefore the one way coupling is considered the most usable, due to its capability to coupled also non-corresponding geometries. |
