Direct Numerical Simulation of Non-Premixed Flame Extinction by Water Spray

Abstract

The interaction of turbulent nonpremixed flames with fine water spray is studied using direct numerical simulations (DNS) with detailed chemistry. The study is of practical importance in fire safety devices that operate in the mist regime, as well as an inexpensive temperature control mechanism for gas turbines. The implemented computational methods for the Lagrangian particle-in-cell spray droplet representation and modified characteristic boundary conditions for spray-laden reacting flows are briefly described. The model configuration is a two dimensional ethylene-air counterflow diffusion flame at moderate strain rate. Laminar and turbulent flame simulations are performed with various water loading conditions. Comparison of various simulation cases highlights the flame weakening characteristics due to fluid dynamic strain and water spray evaporation. A modified mixture fraction variable defined in our earlier study [1] is applied to provide correct physical description of the flame response by accurately capturing the flame locations. Findings from this study provide a better understanding of interaction between thermal and aerodynamic quenching in turbulent flame dynamics.

A computational study of non-premixed flame extinction by water spray

“…The spray droplets are treated in a Lagragian formulation [6], where the drag force is derived by the Stokes law, and the heat conductivity is assumed infinite inside the droplet. The Lagrangian particles are coupled to the Eulerian gas equations through the mass, momentum and energy source terms associated with water evaporation [6,7]. Improved characteristic boundary conditions were also developed to account for spray evaporation effects at the outflow boundaries [7].…”

“…The Lagrangian particles are coupled to the Eulerian gas equations through the mass, momentum and energy source terms associated with water evaporation [6,7]. Improved characteristic boundary conditions were also developed to account for spray evaporation effects at the outflow boundaries [7].…”

“…Details in the computational development of the problems are described in our earlier paper [7], which includes a conservative treatment of coupling between Lagrangian spray droplets and the Eulerian gasphase fluid dynamics, and modified characteristic boundary conditions to account for spray evaporation effects. Recognizing the limitations of the two-dimensional configuration in representing realistic turbulence, the model problem under study allows multiple simulations for parametric investigation at a reasonable computational cost.…”

“…Recent DNS studies [1][2][3][4] have demonstrated that laboratoryscale turbulent flames can be computationally reproduced to yield detailed information of flow and reactive scalar variables with full temporal and spatial resolution, thereby providing valuable insights into the advanced models that can better describe fundamental combustion processes in practical devices. Recent developments by the authors and coworkers in combustion DNS have enhanced the fidelity of underlying physical submodels to describe soot formation, radiative heat transfer, and spray evaporation [5][6][7].…”