Flow topology and alignments of scalar gradients and vorticity in turbulent spray flames: A Direct Numerical Simulation analysis

FUEL

卷:184

Article; Proceedings Paper

Wacks, Daniel¹  Chakraborty, Nilanjan² 

[1] Univ Durham, Sch Engn & Comp Sci, S Rd, Durham DH1 3LE, England

[2] Newcastle Univ, Sch Mech & Syst Engn, Newcastle NE1 7RU, Tyne & Wear, England

关键词: Spray flame;    Turbulence;    Scalar gradient;    Principal strain rate;    Flow topology;   

DOI  :  10.1016/j.fuel.2016.04.061

来源: Elsevier

【 摘 要 】

Flame structure, flow topology and the relative alignments of principal strain rates with scalar gradients and the vorticity vector in turbulent spray flames arising from mono-disperse droplets have been analysed using three-dimensional Direct Numerical Simulations (DNS) data. An extensive parametric analysis has been performed for a range of values of droplet equivalence ratio (phi(d)), droplet diameter (a(d)) and turbulence intensity (u'). The results have been analysed to analyse the statistical behaviours of the alignments of the gradients of mixture fraction and reaction progress variable and of the vorticity vector ((omega) over right arrow) with the local principal strain rates. The resulting alignments of reactive scalar gradient and vorticity with local principal strain rates in droplet-laden flames have been compared to those observed for a gaseous stoichiometric premixed flame under the same turbulent flow conditions. The differences in behaviour have been identified in terms of the statistical behaviours of scalar gradient and vorticity alignments with local principal strain rates in terms of the eight local flow topologies, classified as either focal (four topologies) or nodal (four topologies), in four zones across the flame: leading edge, preheat zone, burning reactants and trailing edge. This information has in turn been utilised to offer detailed physical explanations for the observed differences in alignment statistics of reactive scalar gradient and vorticity between turbulent premixed and spray flames. The implications of scalar gradient and vorticity alignment on the statistical behaviours of scalar-turbulence interaction and vortex stretching terms have been discussed in detail along with explanations for their dependences on droplet size, droplet equivalence ratio and turbulence intensity. (C) 2016 The Authors. Published by Elsevier Ltd.

【 授权许可】

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