On the accuracy of Eulerian-Lagrangian CFD simulations for spray evaporation in turbulent flow

Abstract

CFD simulation of droplet evaporation in turbulent flows is challenging as the accuracy and reliability of the results strongly depend on the available sub-models and their modeling parameters. This study presents a systematic sensitivity analysis focused on the impact of the most widely used discrete random walk (DRW) model, the constant time scale coefficient (C_L), the turbulence model, and the drag coefficient model. CFD simulations with the Eulerian-Lagrangian approach are employed. The analysis is based on grid-sensitivity analysis and validation with measurements of spray evaporation in a heated turbulent airflow. The results show that using the DRW model leads to a good agreement between the CFD results and the experimental data of droplet size and droplet mean velocity, attributed to the turbulent fluctuations inducing droplet dispersion. The best performance is observed for the standard k-ε turbulence model with C_L = 0.30 and 0.45. This is mainly attributed to the reasonable interaction time between droplets and turbulent eddies at these C_L values. The three drag coefficient models (i.e., Spherical, Ischii-Zuber, and Grace) lead to similar results due to the low droplet Reynolds number.