Numerical investigation of a high pressure hydrogen jet of 82 MPa with adaptive mesh refinement: Concentration and velocity distributions

Abstract To investigate the safety properties of high-pressure hydrogen discharge or leakage, an under-expanded hydrogen jet flow with a storage pressure of 82 MPa from a small jet orifice with a diameter of 0.2 mm is studied by three-dimensional (3D) numerical calculations. The full 3D compressible Navier-Stokes equations are utilized in a domain with a size of about 3 × 3 × 6 m which is discretized by employing an adaptive mesh refinement (AMR) technology to reduce the number of grid cells. By AMR, the local mesh resolutions can narrowly cover the Taylor microscale l T and direct numerical simulations (DNS) are performed. Both the instantaneous and mean hydrogen concentration distributions in the present jet are discussed. The instantaneous concentrations of hydrogen C H 2 on the axis presents significant turbulent pulsating oscillations. The centerline value of the intensity of concentration fluctuation σ ˆ H 2 asymptotically comes to 0.23, which is in a good agreement with the existing experimental results. It substantiates the conclusion that the asymptotic centerline value of σ ˆ H 2 is independent of jet density ratio. The probability distributions function (PDF) of instantaneous axial C H 2 agree approximately with the Gaussian distribution while skewing a little to the higher range. The time averaged hydrogen concentration C ¯ H 2 along the radial directions can also be described as a Gaussian distribution. The axial C ¯ H 2 of 82 MPa hydrogen jet tends to obey the distribution discipline approximated with C ¯ H 2 = 4200 / ( z / θ ) where z is the axial distance from the nozzle and θ is the effective ejection diameter, which is consistent with the experimental results. In addition, the hydrogen tip penetration Z tip is found to be in a linear relationship with the square root of jet flow time t . Meanwhile, the jet's velocity half-width L Vh approximately gains an linear relation with z which can be expressed as L Vh = 0.09 z .