Numerical Analysis of Hydrogen Dispersion in Wind Tunnel Modeled on Vehicle Space of Pure Car Carriers

Abstract

Seaborne transportation of hydrogen fuel cell vehicles (HFCVs) by pure car carriers is highly expected to increase due to rising demand for environmental protection in the world. When hydrogen leaks from a HFCV, it may accumulate near the ceiling of a vehicle space, since stiffening members referred to as longitudinal girder, web beams and longitudinal frames act as so-called “smoke barriers”. When carrying out safety assessment of the carriage of HFCVs with possible hydrogen leakage, it is necessary to validate numerical simulation tools to accurately predict ventilation flow properties and hydrogen behavior near the ceiling of a vehicle space. For this purpose, large-eddy simulation (LES) on ventilation flow and hydrogen dispersion in a wind tunnel has been carried out using Fire Dynamics Simulator (FDS), which is one of the well-validated computational fluid dynamics (CFD) codes. The sensitivities of computational grid size and subgrid-scale (SGS) models in the LES technique have been investigated by comparing measurement data. The results indicated that when ventilating the wind tunnel without releasing hydrogen, the present CFD calculations could reproduce the measurement data on velocity profiles without dependence on the SGS models by assigning more than about 10 computational grids to the “smoke barriers” in the depth direction. On the other hand, in the case of ventilation with releasing hydrogen, numerical results with the same grid size considerably underestimated experimental data on hydrogen concentrations. Therefore, care should be taken for the interpretation of real-scale simulation results with relatively coarse, computational grids. The present numerical results also point to a need to improve SGS models in such a way that the effects of stratification of hydrogen/air mixture due to buoyancy can be taken into consideration.