Heat flux and flow topology statistics in oblique and head-on quenching of turbulent premixed flames by isothermal inert walls

ABSTRACT

Direct numerical simulations (DNS) of oblique wall quenching of a turbulent V-flame and head-on quenching (HOQ) of a statistically planar flame by isothermal inert walls have been utilized to analyze the statistics of wall heat flux, flame quenching distance in terms of the distributions of flow topologies and their contributions to the wall heat flux. The flow topologies have been categorized into eight generic flow configurations (i.e., S1–S8) in terms of three invariants of the velocity gradient tensor (i.e., first, second and third P, Q, and R, respectively). It has been found that nodal (i.e., strain rate dominated) flow topologies are major contributors to the wall heat flux when it attains large magnitude in the HOQ configuration, whereas focal (i.e., vorticity-dominated) topologies contribute significantly to the wall heat flux in the case of oblique flame quenching. These differences in the heat transfer mechanisms contribute to the differences in wall heat flux and flame quenching distance between HOQ and oblique quenching configurations. The maximum wall heat flux magnitude in the case of oblique flame quenching has been found to be greater than that in the corresponding turbulent HOQ case. By contrast, the minimum wall Peclet number, which quantifies the flame quenching distance, in the case of oblique quenching has been found to be smaller than that in the case of HOQ.

KEYWORDS:

• Flow topology
• Wall heat flux
• Wall Peclet number
• Oblique flame quenching
• Head-on quenching
• Direct numerical simulations

Acknowledgments

NC is grateful to the Engineering and Physical Sciences Research Council (EPSRC), UK and ARCHER for financial and computational support, respectively.

Notes

¹. The statistics for the OWQ case in this paper are presented at t = 2.39t_ft but the configuration reaches a statistically stationary state since one through pass time (i.e., t = 1.0t_ft) so the statistics remain the same (see Figure 11 where the statistics remain qualitatively the same) for $\mathrm{t}\ge 1.0{\mathrm{t}}_{\mathrm{f}\mathrm{t}}$. Here $\mathrm{t}=2.39{\mathrm{t}}_{\mathrm{f}\mathrm{t}}$ is explicitly mentioned in the figure captions for the purpose of completeness.

Additional information

Funding

This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) [EP/K025163/1 and EP/P022286/1].