Flow and Mixing Fields for Transported Scalar PDF Simulations of a Piloted Jet Diffusion Flame (‘Delft Flame III’)

Abstract

Abstract. Numerical simulation results are presented for 'Delft Flame III', a piloted jet diffusion flame with strong turbulence-chemistry interaction. While pilot flames emerge from 12 separate holes in the experiments, the simulations are performed on a rectangular grid, under the assumption of axisymmetry. In the first part of the paper, flow and mixing field results are presented with a non-linear first order k-ε model, with the transport equation for ε based on a modeled enstrophy transport equation, for cold and reactive flows. For the latter, the turbulence model is applied in combination with pre-assumed β-PDF modeling for the turbulence-chemistry interaction. The mixture fraction serves as conserved scalar. Two chemistry models are considered: chemical equilibrium and a steady laminar flamelet model. The importance of the turbulence model is highlighted. The influence of the chemistry model is noticeable too. A procedure is described to construct appropriate inlet boundary conditions. Still, the generation of accurate inlet boundary conditions is shown to be far less important, their effect being local, close to the nozzle exit. In the second part of the paper, results are presented with the transported scalar PDF approach as turbulencechemistry interaction model. A C 1 skeletal scheme serves as chemistry model, while the EMST method is applied as micro-mixing model. For the transported PDF simulations, the model for the pilot flames, as an energy source term in the mean enthalpy transport equation, is important with respect to the accuracy of the flow field predictions. It is explained that the strong influence on the flow and mixing field is through the turbulent shear stress force in the region, close to the nozzle exit.

Numerical Simulation of Delft-Jet-in-Hot-Coflow (DJHC) Flames Using the Eddy Dissipation Concept Model for Turbulence–Chemistry Interaction

“…5). This is in agreement with the known fact that the RKE performs well compared to SKE in round jet calculations not only for non-reacting turbulent flows [26], but also for reacting turbulent flow calculations [38,39].…”

Conditional Moment Closure/Large Eddy Simulation of the Delft-III Natural Gas Non-premixed Jet Flame

“…The Delft Flame III is also a target in the TNF workshop series (http://www.sandia.gov/TNF). Several attempts have been conducted to model this flame using RANS formulations and various combustion models, including the transported PDF method with reduced and detailed chemistry [14,15,18,20]. Nooren et al [18] and Merci et al [15] have shown that transported PDF results are strongly dependent on the micro-mixing model used, especially in the case of the temperature PDFs, while Merci et al [15] reported that it was not possible to predict accurately both the RMS of the mixture fraction and the amount of local extinction.…”

Analysis of extinction in a non-premixed turbulent flame using large eddy simulation and the chemical explosion mode analysis

“…Despite its moderate Reynolds number, the Delft Flame has strong extinction and significant finite rate chemistry effects. It has only been investigated before by Merci et al [22,23] using RANS-PDF and by Ayache and Mastorakos [2] using a LES-CMC method. The flame is composed of a central fuel jet, surrounded by two concentric coflows of air.…”

“…The main fuel jet is separated from the primary air stream by a rim of outer diameter 15 mm. The pilot flames are located on this rim and consist of 0.5 mm diameter holes located on a circle of 7 mm diameter in order to prevent flame lift-off [22]. The fuel used was commercially available Dutch natural gas (see composition in Table 1) with an adiabatic temperature T ad = 2216 K and a stoichiometric mixture fraction f st = 0.071 [28].…”

“…Several approaches have been proposed in the literature with regards to the modelling of the pilot flames. Merci et al [22,23,24], Roekaerts et al [33] modelled the pilot flames by the local addition of a heat source term, neglecting their negligible mass flow rate and momentum. Ayache and Mastorakos [2] represented the pilot as an annular ring of 1 mm thickness around the fuel jet and this approach has been followed in the present work.…”