Stratified flows and associated shear instabilities modelling over an inclined plan

Abstract We investigate isothermal continuous gravity currents down on an incline of 5°. The front region with strong mixing and the shallower layer behind it are modelled using computational fluid dynamics in order to discuss the dilution process in accidental releases. The simulations were performed using two different customised packages for compressible and a non-compressible flows. The heavy fluid dilution was analysed considering RANS (Reynolds Average Navier Stokes) approach and three turbulence models k − ɛ, k − ω SST and RNG k − ɛ. The simulated gravity currents were compared with experimental by means of the the density distribution in the flow and volume of the current. As far as dense gas cloud prediction is concerned, the numerical findings agree with the experimental data and there seems to be good indication that the solvers are suitable for consequence analysis. Shear instabilities caused by the flow of two fluids near the interface zone are well captured by RNG k − ɛ turbulence model. The simulations show that the modelling of small scale turbulence and associated rate of deformation are important to mimic the wavy instabilities and curling of the interface region of the released and ambient fluid. Such process is of paramount importance when predicting the mixing and dilution of the released material. Analysis of the results shows that better agreement is observed when the proper modelling of the shear instabilities is considered as well as the extra source of turbulence due to the effects of buoyancy.