模型管道几何形状多组分喷射的实验研究及其在氢气安全中的应用

Development of modern safety standards for hydrogen storage infrastructure requires
fundamental insight into the physics of buoyant gas dispersion into ambient air. Also,
from a practical engineering stand-point, flow patterns and dispersion of gas originating
from orifices in the side wall of circular pipe or storage tank need to be studied. In this thesis, novel configurations were considered to investigate the evolution of turbulent jets issuing from realistic pipeline geometries. First, the effect of jet densities and Reynolds numbers on vertical jets were investigated, as they emerged from the side wall of a circular pipe, through a round orifice. The resulting jet flow was thus issued through a curved surface from a source whose original velocity components were nearly perpendicular to the direction of the ensuing jets. Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques were employed simultaneously to provide instantaneous and time-averaged flow fields of velocity and concentration. The realistic flow arrangement resulted in an asymmetric
flow pattern and a significant deflection from the vertical axis of jets. The deflection was influenced by buoyancy, where heavier gases detected more than lighter gases. These realistic jets experienced faster velocity decay, and asymmetric jet spreading compared to
round jets due to significant turbulent mixing in their near field.

    In addition to that, horizontal multi-component jets issuing from a round orifice on the side wall of a circular tube were also investigated experimentally by the means of simultaneous velocity and concentration measurements. A range of Reynolds numbers and gas densities were considered to study the effects of buoyancy and asymmetry on the resulting flow structure. The realistic pipeline jets were always exhibited an asymmetry structure and found to deflect about the jet's streamwise axis in the near field. In the far field, the buoyancy dominated much closer to the orifice than expected in the axisymmetric round jet due to the realistic leak geometry along with the pipeline orientation considered in this study. In general, significant differences were found between the centreline trajectory, spreading rate, and velocity decay of conventional horizontal round axisymmetric jets issuing through
at plates and the pipeline leak-representative jets considered in the present study.
      Finally, the dispersion of turbulent multi-component jets issuing from high-aspectratio
slots on the side wall of a circular tube were studies experimentally by employing
simultaneous PIV and PLIF techniques. Two transversal & longitudinal oblong geometries
in respect to the longitudinal axes of the tube , and with an aspect ratio of 10 were considered in this study. Both horizontal and vertical orientations along with broad range of Reynolds numbers and gas densities were considered to investigate the effects of buoyancy and asymmetry on the resulting flow structure. The ensuing jets were found to deflect along the jet streamwise axis, once more, due to the realistic pipeline leak-representative configuration. It was also found that increases in aspect ratio of these realistic jets caused a reduction in the angle of deflection, jet centreline decay rates and the width growth on both velocity and scalar fields compared to their round jets counterparts, most notably in the far field.
    These ndings indicate that conventional jets (those that are issuing through
at surfaces) assumptions are inadequate to predict gas concentration, entrainment rates
and, consequently, the extent of the ammability envelope of realistic gas leaks. Thus,
extreme caution is required when using conventional jet assumptions to describe the
physics of a buoyant jet emitted from realistic geometries.