Effects of Fuel Lewis Number on the Near-wall Dynamics for Statistically Planar Turbulent Premixed Flames Impinging on Inert Cold Walls

ABSTRACT

The flame-wall interaction in a quasi-steady configuration, where a statistically planar premixed flame is pushed by the inflow of unburned reactants and stabilizes at a distance away from the wall, has been analyzed for different fuel Lewis numbers and inlet turbulence intensities. The extent of flame-wall interaction has been found to increase with increasing inlet turbulence intensity and increasing fuel Lewis number $L{e}_F$ due to the greater extent of flame wrinkling and smaller flame stabilization distance from the wall, respectively. The increasing trend of turbulent flame speed with decreasing fuel Lewis number and increasing inlet turbulence intensity act to increase the wall heat flux magnitude. However, the quenching distance remains comparable to the quenching distance predicted by one-dimensional conventional head-on quenching simulations. It has been found that the wall Stanton number and the skin friction coefficient are of the same order of magnitude, but the Reynolds-Colburn analogy does not remain strictly valid in the case of flame-wall interaction in this configuration. For a given value of bulk mean inlet velocity to laminar burning velocity ratio, the flames with smaller $L{e}_F$ stabilize further away from the wall due to their higher turbulent flame speed and thus the flame-wall interaction events are less frequent for small values of $L{e}_F$. The drops in temperature and reaction rate magnitude lead to reductions in the values of dilatation rate, normal strain rate, and flame displacement speed in the flame quenching zone; with the increased likelihood of finding negative values for these quantities in the near-wall region. The decrease in displacement speed with decreasing wall-normal distance leads to predominantly positive normal strain rates induced by flame propagation in the quenching zone. These behaviors act to reduce the magnitude of the reaction progress variable gradient in the quenching zone, which has implications on the behaviors of the Flame Surface Density and scalar dissipation rate in the near-wall region.

KEYWORDS:

• Flame-wall interaction
• wall heat flux magnitude
• quenching distance
• strain rate
• direct Numerical Simulations

Acknowledgments

The authors are grateful to EPSRC (EP/P022286/1) for the financial support. Computational support was provided by ARCHER (EP/K025163/1, EP/R029369/1) and Rocket (Newcastle University). The authors are also grateful to Mrs. Gulcan Ozel-Erol for her help while preparing this manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors are grateful to the Engineering and Physical Sciences Research Council (EPSRC), UK and ARCHER for financial and computational support, respectively; Engineering and Physical Sciences Research Council [EP/R029369/1, EP/K025163/1];