Numerical calculations of unsteady heavy gas dispersion

摘要

This paper concerns both near-field and far-field numerical predictions of liquefied gas releases in atmospheric environment. The near-field prediction was related to sudden depres-surization of liquefied propane into atmospheric environment. Three phases of propane vapor, propane droplets, and entrained air were considered. Simplification was made that air and vapor have the same velocity and temperature but different volume fractions so that an air-vapor mixture phase could be assumed, and was treated using an Eulerian formulation. The droplet phase was handled using a Lagrangian formulation by which droplet trajectories were computed. A thin-skin evaporation model was used to account for droplet evaporation for the near-field prediction. Present numerical results for the near-field modelling were compared with those obtained with a twin-fluid Eulerian-Eulerian model. The far-field prediction was associated with heavy gas dispersion of Burro 8 LNG field test in a flat terrain. The conventional κ-ε eddy viscosity-diffusivity model was modified to account for the anisotropy of turbulence characterized by heavy gas dispersion close to a ground. Numerical results were presented for the Burro 8 LNG field test. Results for the far field simulation were also compared with those obtained with the commercial code DEGADIS.