Quantitative Imaging of Multi-Component Turbulent Jets

The integration of a hydrogen gas storage arrangement in vehicles has not been without its challenges. Gaseous state of hydrogen at ambient temperature, combined with the fact that hydrogen is highly flammable, results in the requirement of more robust, high pressure storage systems that can meet modern safety standards. To develop these new safety standards and to properly predict the phenomena of hydrogen dispersion, a better understanding of the resulting flow structures and flammable region from controlled and uncontrolled releases of hydrogen gas must be achieved. With the upper and lower explosive limits of hydrogen known, the flammable envelope surrounding the site of a uncontrolled hydrogen release can be found from the concentration field. In this study the subsonic release of hydrogen was emulated using helium as a substitute working fluid. A sharp orifice round turbulent jet is used to emulate releases in which leak geometry is circular. Effects of buoyancy and crossflow were studied over a wide range of Froude numbers. The velocity fields of turbulent jets were characterized using particle image velocimetry (PIV). The mean and fluctuation velocity components were well quantified to show the effect of buoyancy due to the density difference between helium and the surrounding air. In the range of Froude numbers investigated (Fr = 1000, 750, 500, 250 and 50), the increasing effects of buoyancy were seen to be proportional to the reduction of the Fr number. While buoyancy is experienced to have a negligible effect on centerline velocity fluctuations, acceleration due to buoyancy in the other hand resulted in a slower decay of time-averaged axial velocity component along the centerline. The obtained results will serve as control reference values for further concentration measurement study and for computational fluid dynamics (CFD) validation.