CFD Based Simulation of Hydrogen Release Through Elliptical Orifices

Computational Fluid Dynamics (CFD) is applied to investigate the near exit jet behavior of high pressure hydrogen release into quiescent ambient air through different types of orifices. The size and geometry of the release hole can affect the possibility of auto-ignition. Therefore, the effect of release geometry on the behavior and development of hydrogen jet issuing from non-axisymmetric (elliptical) and expanding orifices is investigated and compared with their equivalent circular orifices. A three- dimensional in-house code is developed using the MPI library for parallel computing to simulate the flow based on an inviscid approximation. Convection dominates viscous effects in strongly under- expanded supersonic jets in the vicinity of release exit, justifying the use of the Euler equations. The transport (advection) equation is applied to calculate the concentration of hydrogen-air mixture. The Abel-Nobel equation of state is used because high pressure hydrogen flow deviates from the ideal gas assumption. This work effort is conducted to fulfill two objectives. First, two types of circular and elliptic orifices with the same cross sectional area are simulated and the flow behavior of each case is studied and compared during the initial stage of release. Second, the comparative study between expanding circular exit and its fixed counterpart is carried out. This evaluation is conducted for different sizes of nozzle with different aspect ratios.