Numerical Investigation of the Cryogenic Underexpanded Hydrogen Jets Exiting Rectangular Shaped Openings

Abstract

Cryo-compressed hydrogen shows increasing potentials in hydrogen utilization. The development and revision of safety codes and standards for cryo-compressed hydrogen infrastructure requires studies of accidental leaks for various scenarios. However, the actual leaks are more likely to result in jets through slots rather than round nozzles in most previously studies. In this work, a numerical model of cryogenic hydrogen underexpanded jets was built to evaluate the effect of jet temperature and aspect ratio of rectangular nozzles on the shock structure and dispersion characteristics. The numerical results revealed that cryogenic hydrogen release caused axial extension of the hazard zone. The normalized radial volume fraction of various jet temperature collapsed into a Gaussian distribution. The aspect ratio of rectangular nozzle shows significant effect on the shock structure and hydrogen dispersion. The shock intensity decreases with aspect ratio and Mach disk disappear when the ratio larger than eight. The effect of nozzle shape on hydrogen diffusion was pronounced at high pressure ratio between nozzle exits and environment. The normalized volume fraction on centerline decay rates increased with the aspect ratio. And that on the minor axis plane did not fit a Gaussian distribution when the aspect ratio was larger than eight due to axis switching, which also produced a wider hazard zone.

Keywords: Cryogenic hydrogen, Underexpanded jets, Shock wave, Hydrogen dispersion, Rectangular nozzle