OpenFOAM-based study on near-field formation and mixing of high nozzle pressure ratio hydrogen jets from leakages

A gas stored at high-pressure leaking through a small hole forms a complex series of shock structures as it accelerates and expands to ambient conditions. The near-field region of the jet includes the initial jet expansion, Mach disc formation, and starting vortices, all of which can affect hydrogen mixing with the surrounding air and have an associated combustion risk. Through the use of a modified OpenFOAM solver, simulations of hydrogen stored at 10 bar and 100 bar leaking into atmospheric conditions through 1.5 mm diameter circular nozzles were performed to determine the transient temperature profile, shock locations, and hydrogen mixing profiles of the hydrogen jet in its initial expansion and propagation stages. From these transient simulations, it was shown that starting vortices form pockets of mixed hydrogen and air that are within hydrogen flammability limits. This new simulation data shows mixed hydrogen pockets can linger in the nozzle near-field region and present a flammability risk that is not easily accounted for when using existing numerical models optimized for far-field flame behavior, showing this new open-source tool can resolve hydrogen mixing behavior in the nozzle near-field region without compromising on shock resolution capabilities. • Existing OpenFOAM solver modified to simulate high-pressure hydrogen leaks. • Transient numerical data for the highly-underexpanded hydrogen jets captured. • Mixing vortices are observed to shed pockets of mixed hydrogen and air. • Potentially flammable hydrogen pockets observed to linger near the nozzle.