Vertical Turbulent Buoyant Helium Jet - CFD Modelling and Validation

In this paper, a vertical turbulent round jet of helium was studied numerically using the PHOENICS software package. The flow was assumed to be steady, incompressible and turbulent. The jet discharge Froude number was 14,000 and the turbulent Schmidt number was 0.7. The incompressible Reynolds average Navier-Stokes equations and helium transport equation expressed in 2-D axisymmetric domain were applied to model the underlying helium release. The k-e RNG turbulence model was used for the calculations of the corresponding turbulent viscosity, diffusivity, velocity and concentration fields in the domain. The simulation results are compared with the experimental measurements from the earlier published studies on helium jets in non-buoyant jet region (NBJ), intermediate region (I) and buoyant plume region (BP). The numerical results show that the radial profiles of mean velocity and mean concentration are consistent with the empirical data scaled by the effective diameter and density-ratio dependence. The mean velocity and concentration fields along the axis of the jet agree with the decay laws correlated from the previous experiments. The discrepancy between the numerical and experimental data is within 10%, proving that the current CFD model for gas release and dispersion is robust, accurate and reliable, and that the CFD technique can be used as an alternative to the experiments with similar helium jets. The authors believe that the current CFD model is well validated through this study and can be further extended to predict similar hydrogen releases and dispersion if the model is properly applied with hydrogen properties.