Scalar Gradient and Strain Rate Statistics in Oblique Premixed Flame–Wall Interaction Within Turbulent Channel Flows

Abstract

Three-dimensional direct numerical simulations of V-flames interacting with chemically inert walls in a fully developed turbulent channel flow have been performed under adiabatic and isothermal wall boundary conditions using single-step chemistry. These simulations are representative of stoichiometric methane-air mixture at unity Lewis number under atmospheric conditions. The turbulence in the non-reacting channel is representative of the friction velocity based Reynolds number $$Re_{\tau }=110$$ R e τ = 110 . Differences in the statistical behaviours of the mean values of progress variable, temperature, and density have been reported for different wall boundary conditions. It is found that the mean location of the oblique flame interacting with the wall is affected by the choice of the wall boundary condition used. The influence of these differences on the flame dynamics is investigated by analysing the statistical behaviours of the surface density function (SDF) and the strain rates, which govern the evolution of the SDF. The mean variation of the SDF and the flame displacement speed are strongly affected by the wall boundary condition within the viscous sub-layer region of the boundary layer. The behaviours of the normal and tangential strain rates are found to be influenced by not only the differences in the wall boundary conditions, but also by the distance from the wall. The differences in the displacement speed statistics for different wall boundary conditions and wall distance affect the behaviours of the normal strain rate arising due to flame propagation and curvature stretch. The changes in the SDF behaviour in the near wall region have been explained in terms of the statistics of effective normal strain rate experienced by the progress variable iso-surfaces under different wall boundary conditions and wall normal distances.

Computational Study of Premixed Flame Propagation in Micro-Channels with Nonslip Walls: Effect of Wall Temperature

“…In particular, isothermal and adiabatic walls provide qualitatively different flame shapes. Such a result agrees with the recent findings of Ahmed et al [23,24], who also found that the shapes of the oblique premixed turbulent flame fronts in the near-wall region differ for the isothermal and adiabatic walls; see Reference [24] and references therein for more details.…”

“…These interactions occur in many engineering applications such as spark-ignition engines, gas turbines, etc., with the walls playing an important role in the formation of the turbulent structures and, consequently, in the combustion process. Ahmed et al [23,24] investigated the interaction of oblique flames with adiabatic and isothermal walls by performing the DNS of the V-shaped flames developed in a channel flow. Additionally, the V-flame in the adiabatic case presented the features of the aerodynamic quenching.…”

“…Additionally, the V-flame in the adiabatic case presented the features of the aerodynamic quenching. This study discussed how the isothermal or adiabatic walls influence the flame shape in the near-wall region; see Reference [24] and references therein for details. In particular, the results [23,24] showed that the thermal wall conditions slightly modified the location of the oblique flame-wall interaction.…”

“…This study discussed how the isothermal or adiabatic walls influence the flame shape in the near-wall region; see Reference [24] and references therein for details. In particular, the results [23,24] showed that the thermal wall conditions slightly modified the location of the oblique flame-wall interaction. The studies [23,24] also included extensive comparison of the mean quantities such as the turbulent kinetic energy as well as the dissipation rate and the mean reaction rate for the adiabatic and isothermal wall conditions.…”

Influence of Thermal Expansion on Fluid Dynamics of Turbulent Premixed Combustion and Its Modelling Implications

“…in hybrid engines) are now made smaller in size and increased popularity of microcombustors has increased the importance of premixed flame-wall interactions for combustion modellers. Recent analyses on turbulent premixed flame-wall interaction suggest that the decrease in dilatation rate either due to flame quenching as a result of wall heat loss or due to wall-induced confinement can have a significant influence on enstrophy (Lai et al 2017a), turbulent kinetic energy (Lai et al 2017b;Ahmed et al 2019c), turbulent scalar flux (Lai et al 2017c), scalar variance (Lai and Chakraborty 2016a) and reactive scalar gradient statistics (Sellmann et al 2017;Lai and Chakraborty 2016b, c, d;Ahmed et al 2020;Bruneaux et al 1997) in the near-wall region. Moreover, the usual log-law for mean velocity and temperature variations is often rendered invalid during turbulent premixed flame-wall interactions (Bruneaux et al 1997(Bruneaux et al , 1996Jainski et al 2018).…”