Abstract

Computational Fluid Dynamics (CFD) is employed to investigate the near exit jet behavior of a high-pressure hydrogen release into the quiescent ambient air through different types of orifices. The effect of orifice geometry on the structure, development and dispersion of highly under-expanded hydrogen jet is numerically investigated. Various shapes of orifices are evaluated including holes with constant areas such as elliptical and circular openings, and deforming apertures under different configurations and conditions considering the interactions of enlarging of circular openings and the release time, as well as the deformation of a circular hole to an elliptical hole. A three-dimensional in-house parallel code is exploited to simulate the flow using an unstructured tetrahedral finite volume Euler solver. The transport (advection) equation is applied to track the shape and the location of the hydrogen - air interface. The Abel-Nobel real gas law is used since high-pressure hydrogen flow deviates from the ideal gas assumption. Comparative studies between the dispersion of hydrogen jet issuing from different types of orifices in terms of jet development and pressure expansion are carried out. The numerical simulations indicate that in addition to the hydrogen storage pressure, the shape and the size of the orifice influence the hydrogen jet development which can affect the ignition risks associated with the accidental release of hydrogen.