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CFD simulations in Tunnels

The k- atmospheric dispersion model POLLUT was used in a DLR study (EichertH:1992) to investigate hydrogen dispersion from accidental release of LH2 from vehicle tanks in a road tunnel.

Simulations of hydrogen releases from LH2 and CGH2 private vehicles (cars) in a naturally ventilated tunnel were reported by Wilkening et al. (WilkeningH:2000). The work was performed within the framework of the EIHP project (EIHP:url). The ADREA-HF code was used for the dispersion calculations. The REACFLOW code was used for the combustion calculations. Two LH2 release scenarios were considered. A flow restrictor installed and a two-phase release of 8.3 g/s was assumed in the first scenario. A shut-off valve activated 5 seconds after the release and a gaseous release of 60g/s was considered in the second. For the CGH2 scenario sonic release from a 200bar storage tank was assumed. The reported overpressure results indicated that for the scenarios considered there is no major difference in using liquid hydrogen or compressed hydrogen fuel.

Tunnel accidents with an LH2 powered vehicle were simulated by Breitung et al. (BreitungW:2000). The investigated scenarios assume damage of the LH2 system, release of gaseous hydrogen, mixing with air, ignition and finally combustion. Calculations showed that gaseous hydrogen rises to the tunnel ceiling forming a strongly stratified mixture. Shape, size, inner structure and temperature of the evolving H2-air cloud were calculated. Using new developed criteria, the time and space regions with potential for fast combustion modes were identified. For the given hydrogen sources the combustion regime is governed by the ignition time. For late ignition a slow and incomplete combustion of the partly premixed H2-air cloud along the tunnel ceiling was predicted. For early ignition a standing diffusion flame develops with dimensions and heat fluxes determined by the hydrogen release rate. Temperature, oxygen and flow velocity fields during the combustion were computed. In both cases only minor pressures were generated. The highest damage potential appeared to exist for intermediate ignition times.

Simulations of hydrogen releases from CGH2 commercial vehicles (busses) in tunnel environment were reported by (VenetsanosAG:2008). The work was performed during the EIHP2 project (EIHP:url), using the ADREA-HF code for dispersion and the REACFLOW code for combustion. Three different storage pressures were considered for the CGH2 releases 200, 350 and 700 bar. Compartive simulations were performed for a 200bar CNG bus.

CFD simulations of hydrogen dispersion in tunnels was performed by (MukaiS:2005), using the STAR-CD code and standard k-ε model. The amount of hydrogen leaked was 60 m3 (approximately 5.08 kg), which corresponds to the amount necessary for future fuel cell vehicles to achieve their desired running distance. The study considered the typical longitudinal and lateral areas of tunnels, the undergound ventilation facilities and the electrostatic dust collectors.

References

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