DNS of Unsteady Flame-Wall Interaction

Direct numerical simulations (DNS) of unsteady side-wall quenching (SWQ) of stoichiometric premixed methane/air flames operated at atmospheric condition have been conducted. Objective of the work is to study the effect of transient, relative motion between the flame and the wall on the flame-wall interaction (FWI). A W-shaped plane-jet flame is considered, which is bounded in its lateral direction by two side walls. The unsteady motion of the flame is generated by using an oscillatory wall moving in its normal direction, with a pre-defined frequency $f$ and stroke length $L$ (distance between min/max wall normal locations). It has been found that the time-mean quenching distance $d_q$ and wall heat flux $\overline{\dot{q}}_w$ increase strongly with $f$ and $L$. In the case of weak flow disturbances with small $f$ and $L$, $d_q$ and $\overline{\dot{q}}_w$ yield a quasi-linear correlation with each other. However, a hysteresis loop for the correlation of $d_q$ and $\overline{\dot{q}}_w$ has been confirmed with increased $f$ and $L$, which is attributed to the delayed response of the flame to the unsteady fluctuations of the flow and temperature fields. ... mehrThe behaviour of the flow-flamewall interaction has been revealed: the unsteady flow disturbance results in a relative motion between the flame and the wall. As a consequence, $d_q$ fluctuates in time, which leads to a different $\overline{\dot{q}}_w$ or heat loss sensed by the flame. The flame adjusts its dynamics (movement) with updated $\overline{\dot{q}}_w$ and the loop starts over again. The results indicate the strong impact of the unsteady flow on the FWI phenomena, which leads to delayed response of FWI to the unsteadily moving flame and modified quenching distance as well as wall heat fluxes.