Figure 2. Key elements of the smoke exhaust system. Figure 3. Comparison between the HRR curve produced with a tray of size A2 and the curve of the ignition model 5. Table |. Maximum temperature in the thermocouple trees. Numerical simulations Figure 9. Curve of the estimated results of visibility at 1.7 m height (the results of GP-2 and GP-3 are superimposed). computational domain has a length of 42 m, a width of 2.7 m and a height of 2.2 m. At the beginning of the simulation, the air temperature inside of the car is 34°C, outside of the car is 24°C (same measured during the tests) and it is at atmospheric pressure. Figure 10 shows the representation of the train in FDS model. AEPOoeMlallOll OL US Uidill Tit PLO MIO. For simulations involving buoyant plumes, a measure of how well the flow field is resolved is given by the non-dimensional expression (D*/6,.), where D* is a characteristic fire diameter and 6, is the nominal size of a mesh cell.'*??7? (D*/5,.) can be also understood as the number of computational cells spanning the characteristic (not necessarily the physical) diameter of the fire. The more cells spanning the fire, the better the resolution of the calcula- tion. It is highly recommended this coefficient to have a value between 4 (coarse mesh) and 16 (fine mesh).**° In this case, the grid size was selected to be 0.1 m, because with a heat release rate (HRR) of 140 kW, the obtained coefficient value is 4.37. Lc a : , , oy, ey i i | iy oy i ey ie Figure I 1. Longitudinal slice of temperature by the centre of the train in FDS model: (a) 100 s, (b) 200 s and (c) 300 s. Figure 12. Longitudinal slice of visibility by the centre of the train in FDS model: (a) 100 s, (b) 200 s and (c) 300 s. Figure 13. Longitudinal slice of temperature by the centre of the train in FDS model: (a) 100 s, (b) 200 s, (c) 300 s and (d) 600 s. Figure 14. Longitudinal slice of visibility by the centre of the train in FDS model: (a) 100 s, (b) 200 s, (c) 300 s and (d) 600 s. During the tests, it can be observed how temperature increases greater than 30°C at heights higher than 1.5 m, with the only exception of the tree closest to the ignition source (A_3) at the time instant of 300 s, when this tree has a temperature increase of 60°C at that height. However, the simulation provides higher increases at temperature of 30°C for all points higher than | m and greater heating of the lower zones is observed. The A_3 tree simulation also reaches higher temperatures than the experimental test at lower heights, which may be caused by differences j in the HRR definition. ae. Bae ae oh ae ae - gel
