Numerical modelling of the interaction between water sprays and hot air jets - Part I: Gas phase Large Eddy Simulations

The paper reports a comprehensive set of large-eddy simulations (LES) of a turbulent hot air jet impinging onto a ceiling. The hot air source is a 72-mm diameter circular nozzle with an exit temperature maintained at 205 °C. Three exit velocities have been tested: 3.3, 4.2 and 5.3 m/s, corresponding to Reynolds numbers of respectively 6800, 8600 and 10900 and Froude numbers of respectively 3.9, 5.0 and 6.3. The horizontal aluminium ceiling plate of 1.22 m × 1.22 m has been placed at a distance of 590 mm above the hot air nozzle. This configuration has been examined experimentally by Zhou [Proceedings of the Combustion Institute, 2015] to characterize gas phase conditions prior to experiments which aim at studying the interaction between hot air jets and water sprays. This paper constitutes the first part of a numerical study that aims at assessing the current modelling capabilities of the two-phase flow configuration examined by Zhou [Proceedings of the Combustion Institute, 2015]. The results show that the centerline mean vertical velocity profiles of the vertical jet are predicted with maximum deviations of less than 6% from the experimental data at the condition of an appropriate set-up of the inflow conditions (i.e., geometry of the inlet and turbulence inflow boundary conditions). Furthermore, the best results were obtained with the dynamic Smagorinsky model for the turbulent viscosity. The modified Deardorff results are nevertheless very good given the substantial decrease in computational time (in comparison to the dynamic Smagorinsky model). A good prediction of the vertical jet allowed relatively good predictions of the ceiling jet maximum velocity, boundary layer thickness and Gaussian momentum width with maximum deviations of respectively 20%, 1 mm and 18%. The numerical modelling of the gas phase described in this paper can thus be relied upon in the two-phase simulations described in the companion paper [Part II: Two-phase flow simulations].