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Large eddy simulations of unconfined non-reacting and reacting turbulent low swirl jets

Shahsavari, M ; Sharif University of Technology | 2017

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  1. Type of Document: Article
  2. DOI: 10.1007/s10494-016-9790-x
  3. Publisher: Springer Netherlands , 2017
  4. Abstract:
  5. The low swirl flow is a novel method for stabilizing lean premixed combustion to achieve low emissions of nitrogen oxides. Understanding the characteristics of low swirl flows is of both practical and fundamental interest. In this paper, in order to gain better insight into low swirl stabilized combustion, large eddy simulation and dynamically thickened flame combustion modeling are used to characterize various features of non-reacting and reacting low swirl flows including vortex breakdown, shear layers’ instability, and coherent structures. Furthermore, four test cases with different equivalence ratios are studied to evaluate the effects of equivalence ratio on the flame and flow characteristics. A finite volume scheme on a Cartesian grid with a dynamic one equation eddy viscosity subgrid model is used for large eddy simulations. The obtained results show that the combustion heat release and increase in equivalence ratio toward the stoichiometric value decrease the local swirl number of the flow field, while increasing the flow spreading at the burner outlet. Results show that the flame becomes W shaped as the equivalence ratio increases. Moreover, the combination of the swirling motion and combustion heat release temporally imposes a vortex breakdown in the post-flame region, which leads to occurrence of a transient recirculation zone. The temporal recirculation zone disappears downstream of the burner outlet due to merging of the inner shear layer from all sides at the centerline. Also, various analyses of shear layers’ wavy and vortical structures show that combustion heat release has the effect of decreasing the instability amplitude and vortex shedding frequency. © 2016, Springer Science+Business Media Dordrecht
  6. Keywords:
  7. Coherent structures ; Large eddy simulation ; Premixed low swirl flame ; Thickened flame model ; Vortex breakdown ; Combustion ; Nitrogen oxides ; Shear flow ; Vortex flow ; Coherent structure ; Finite volume schemes ; Flow charac-teristics ; Lean premixed combustion ; Low swirl ; Thickened flames ; Vortex shedding frequency ; Flame research
  8. Source: Flow, Turbulence and Combustion ; Volume 98, Issue 3 , 2017 , Pages 817-840 ; 13866184 (ISSN)
  9. URL: https://link.springer.com/article/10.1007/s10494-016-9790-x