Numerical modelling of the interaction between water sprays and hot air jets - Part II: Two-phase flow simulations

Publication date: March 2018
Source:Fire Safety Journal, Volume 96
Author(s): Tarek Beji, Setareh Ebrahimzadeh, Georgios Maragkos, Bart Merci
The paper presents a comprehensive set of numerical simulations performed to examine the current Computational Fluid Dynamics (CFD) capabilities in the prediction of the interaction of a water mist spray with a vertical upward jet of hot air within an Eulerian-Lagrangian framework. The experimental tests considered herein are described by Zhou [Proceedings of the Combustion Institute, 2015]. The spray is a 30° full cone water mist spray emerging from a nozzle that delivers a water flow rate of 0.084 lpm at a pressure of 750 kPa. The vertical jet of hot air at 205∘C is issued from a 72 mm-diameter nozzle placed at 560 mm below the water spray nozzle. Three exit velocities of 3.3, 4.2 and 5.3 m/s were examined. Gas phase simulations (described in the companion paper, Part I) have allowed to determine a set of parameters (e.g., cell size of 4 mm and modified Deardorff model for the turbulent viscosity) that are suitable for the water mist spray simulations. Moreover, it is shown here that a prescribed complex spray pattern with a full discharge angle of 60° is required in order to match water spray profiles in the nozzle near-field. The three regimes of spray-jet interaction (i.e., water spray dominated, vertical jet dominated or equal influence of the spray and the vertical jet) are qualitatively well captured by the numerical simulations. However, the location of the interaction boundary is underestimated by up to 26%. This could be partially attributed to modelling aspects related to, for example, turbulent dispersion or turbulence inflow conditions of the droplets. Uncertainties in the experimental measurements must also be considered.



http://ift.tt/2GKWVhQ