Simulations of Evaporating Spray Jet in a Uniform Co-Flowing Turbulent Air Stream

Abstract

Numerical simulations are performed on the flow of fine, polydisperse droplets of acetone ejected from a round jet of air into an ambient turbulent, uniform co-flowing air stream. The objective is to validate the numerical model by comparing the predictions with experimental measurements of a well defined evaporating spray configuration (Chen et al., Int. J. Multiphase Flow 32(2006), 389–412). The carrier-phase is considered in the Eulerian context, while the dispersed phase is tracked in the Lagrangian framework. Various interactions between the two phases are taken into account by means of a two-way coupling. The stochastic separated flow (SSF) model is adopted for the spray calculations. The gas-phase turbulence terms are closed using the standard k-ε model. The spray evaporation is described using a thermal model with an infinite-conductivity. Overall, very good agreement is observed in the comparisons of the computational predictions and experimental measurements. The predicted droplet number-mean axial velocity, r.m.s. of fluctuating velocity for the various droplet classes at different downstream locations exhibit a self-similarity downstream of the nozzle exit. Near the nozzle-exit (around z/djet = 5), the r.m.s. of droplet number mean axial fluctuating velocity attains a maximum within the shear layer near r/djet = 0.4–0.6 for different droplet classes. Further downstream, the peak shifts towards the axis. A similar variation is noticed in the Sauter mean diameter (SMD) distribution of the droplets. It is concluded that, a higher level of turbulence leads to a faster depletion of the smaller droplets, resulting in an increase in the local droplet-SMD in those regions.