Intro­duc­tion

IFAB pro­duces CFD sim­u­la­tions for defin­ing the design fire curves (HRR) for rail vehi­cles. Alter­na­tive­ly, exper­i­men­tal fire tests can be car­ried out, which is usu­al­ly asso­ci­at­ed with sig­nif­i­cant­ly high­er costs.

Mod­el­ling

Detailed CFD mod­els will be gen­er­at­ed for the stud­ied rail car type. The mod­el is used to sim­u­late spe­cif­ic fire sce­nar­ios in order to deter­mine the heat release curve as func­tion of time.
In order to allow for a sim­u­la­tion using CFD, the mod­el has to be dis­cretized; in this case using cuboid cells. The mod­el is based on the detailed design with a suf­fi­cient res­o­lu­tion and is often based on a very small cal­cu­la­tion grid.
Both out­er struc­tures and inner design are mod­elled in detail to sim­u­late the fire devel­op­ment in a real­is­tic fash­ion. Sim­pli­fi­ca­tions to the geom­e­try or oth­er dis­creti­sa­tion sizes are lever­aged to decrease com­pu­ta­tion time. The influ­ence of said sim­pli­fi­ca­tions on the sim­u­la­tion result is indi­vid­u­al­ly and pre­cise­ly eval­u­at­ed in order to pre­vent a sig­nif­i­cant alter­ation of the results caused by dis­creti­sa­tion fail­ures.

Deter­mi­na­tion of mate­r­i­al para­me­ters

The accu­rate imple­men­ta­tion of indi­vid­ual mate­r­i­al prop­er­ties and para­me­ters is cru­cial in order to achieve good results. For this rea­son, mate­r­i­al sam­ples of the inte­ri­or and exte­ri­or of the rail car have to be pro­vid­ed. These sam­ples are test­ed in a cone calorime­ter. The heat release rate as well as oth­er para­me­ters such as the heat­ing val­ue, igni­tion tem­per­a­ture and smoke pro­duc­tion are deter­mined with this pro­ce­dure.

Deter­mi­na­tion of igni­tion posi­tion

The igni­tion posi­tion is cru­cial and can influ­ence the fire behav­iour sig­nif­i­cant­ly. Mul­ti­ple igni­tion posi­tions that are like­ly to pro­duce dif­fer­ent out­comes in regards to the fire spread behav­iour, are deter­mined and eval­u­at­ed. The igni­tion source can rep­re­sent a burn­ing piece of lug­gage, which is posi­tioned at dif­fer­ent places, for exam­ple under­neath a seat or in the gang­way. The flame spread, smoke gen­er­a­tion, tem­per­a­ture-, and pres­sure fields are used in order to assess the plau­si­bil­i­ty of the result­ing design fire curves.

Ref­er­ences

IFAB was con­tract­ed by the Berlin pub­lic trans­port sys­tem (BVG) to cre­ate a design fire curve for the metro vehi­cle types H and HK (large and small pro­file). This devel­oped curve is used as a design fire curve for the smoke and evac­u­a­tion sim­u­la­tions in all BVG sta­tions in the future. The design fire curve is based on 4 dif­fer­ent pos­si­ble sce­nar­ios that all were sim­u­lat­ed. The results of the most suit­able sce­nario were cho­sen in order to cre­ate the final design curve.