transport of dangerous goods and risk management - Kirilo Savić

TRANSPORT OF DANGEROUS GOODS AND RISK MANAGEMENT 115From Figure 2 one can see, that the left tube is disadvantagues because of negative gradient which will causebuoyancy of the gases against the traffic flow.Fire simulation point in the computational approachVentilat. section DL= 450 m1459 mLeft Tube40 MW+0.90%Fire in 3 sections40 MWA= 82 m 2100 100 1503 lanes-2.2%120 90 90 90Ventilat. section A Ventilat. section B Ventilat. section CH40 MW-0.50%Fire in 3 sections3 lanes40 MWRight Tube +2.2A= 82 m 2124 189 150120 90 90Ventilat. section EVentilat. section FVentilat. section GFansFire points1487 mFigure 3. Road-traffic plan of tunnel with experimentally positioned fires placeTherefore, the left tube of the “Sentvid”-tunnel that is passing under the Slovenian Capital of Ljubljana, was takenas object of interest – both in physical simulations and computational approaches (with the fires sized as 1,5MWand 3,5MW) as well as in the subsequental computational-only experiment of the 40MW-fire. The tunnel itself,with the slope of 2,2 %, has two major main-curves of a Radius of 4000m and 1500m with both “horse-shoe”-cross-section and rectangular- cross-section, where first one is determining first 1080m of the tunnel. Starting as athree-lanes-tunnel, after the bifurcation in “Sentvid” (on the 720 th meter of it´s length) the “main stream” of the“horse-shoe-shaped” tunnel is “continuing” as two-lane traffic communication, the “horse-shoe-shaped” form isexiting and elevating to the point about 12m above road-level of the “main stream”, having the length of further400m and changing from a one-lane to the two-lane “horse-shoe-shaped” cross-section. So, the Aspect-Ratio waschanging in this tunnel: for three-lanes part Ap =1,707 to the rectangular and other horse-shoe-shaped part withtwo lanes with Ap = 1,32.TURBULENCE TREATMENT WITHIN THE CFD-BASED APPROACHThe flow phenomena within the object of interest are computed by the Reynolds Averaged Navier-Stokes (RANS)equations, with the turbulence k- model 19 , representing the major characteristic of the applied CFD-investigationtoolwith the FLUENT. Observations show the Mach Number to be of the order of 0.035 and such a flow can beassumed as incompressible 20 where the combustion makes no impact onto flow-velocity 3 . Further assumption, tohave a planar propagation front of combustion in a motionless fluid, applies here the Boussinesq approximation 21,22without external forces 23 obeying the incompressible Navier-Stokes equation 24 with a temperature-dependent forceterm 23 where the temperature-change describes the advection-reaction-diffusion equation: