CFD benchmark on hydrogen release and dispersion in a ventilated enclosure: Passive ventilation and the role of an external wind

In the framework of the H2FC project a Computational Fluid Dynamics (CFD) benchmarkwas performed to study the release and dispersion of hydrogen in a naturally ventilatedenclosure with one vent. The benchmark involved comparing CFD model predictions withmeasurements from an experiment carried out by the Health and Safety Laboratory (HSL).A total of 28 experiments were performed by HSL using their 31 m3 enclosure and test 25was chosen for this benchmark. In test 25, hydrogen was released vertically upwardsthrough a 0.55 mm diameter nozzle located 0.5 m above the center of the floor of theenclosure. The release was sonic with a volume release rate of 169 NL/min. HSL's experimentalfacility is exposed to naturally varying wind conditions. During test 25 the windblew from the opposite side of the enclosure to the vent at an average speed of 2.6 m/s.Three H2FC partners participated in the benchmark, with three different CFD codes,(ANSYS CFX, ADREA-HF and ANSYS FLUENT) and two different turbulence models (standardk-ε and LES with Smagorinski-Lilly model). In general, satisfactory agreement wasfound between predicted and measured hydrogen concentrations. However, the k-ε modeloverestimates the hydrogen concentration at most of the sensors, while the LES modelunderestimates it, especially at the bottom sensors. Two additional cases with lower windspeed and with no wind were examined. They show that the presence of an external windcan influence the hydrogen dispersion inside an enclosure with one vent. In particular,they show that an external wind can disrupt the buoyancy-driven exchange flow through avent and lead to less efficient ventilation.