NUMERICAL MODELING OF TURBULENT JET DIFFUSION FLAMES IN THE ATMOSPHERIC SURFACE-LAYER

The evolution of turbulent jet diffusion flames of natural gas in air is predicted using a finite-volume procedure for solving the flow equa tions. The model is three dimensional, elliptic and based on the conse rved-scalar approach and the laminar flamelet concept. A laminar flame let prescription for temperature, which is in agreement with measureme nts in methane/air flames and accounts for radiative heat losses, has been modified and adapted to natural-gas flames. The k-epsilon-g turbu lence model has been used. Different probability-density functions for the conserved scalar and an alternative method which does not require the use of a pdf are employed. The model has been applied to flames i n the buoyancy-momentum transition regime, in both cases where the fue l jet is immersed in a co-flowing or in a cross-flow air stream whose properties correspond to the atmospheric surface layer. Experiments ha ve been carried out for a horizontal flame in a wind tunnel with simul ated atmospheric boundary layer, and measurements of temperature distr ibutions are compared with the numerical results; a good agreement is found. The influence of wind properties on flame shape has been invest igated. For horizontal flames, a correlation is proposed for the stoic hiometric flame length as a function of the Froude number and the wind to jet velocity ratio. Flame length predictions have been compared wi th available experimental data and correlations proposed in the litera ture.