On the evolution of turbulent boundary layers during flame-wall interaction investigated by highly resolved laser diagnostics

The turbulent boundary layer behavior in the presence of flame-wall interactions (FWI) has an important role on the mass and energy transfer at the gas/solid interface. Detailed experiments resolving the turbulent boundary layer evolution in the presence of FWI are lacking, which impedes knowledge. This work presents a combination of particle image velocimetry (flow field), dual-pump coherent anti-Stokes Raman spectroscopy (gas temperature), and OH laser induced fluorescence (flame topology) measurements to study the evolution of the boundary layer structure in the presence of FWI. Experiments are conducted in a side-wall quenching (SWQ) burner. Findings reveal that the reacting boundary layer flow adheres to the linear scaling law u⁺ = y⁺ in the viscous sublayer until y⁺ = 5. Beyond y⁺ = 5, the flame modifies the velocity and temperature field such that the u_z⁺ streamwise velocity deviates from the viscous sublayer and the law-of-the-wall scaling in the log-layer with u_z⁺ being smaller than that of the non-reacting flow (the subscript z refers to the streamwise coordinate and is used throughout this manuscript). As the fluid approaches the flame impingement location at the wall, the gas temperature increases significantly, causing a threefold increase in kinematic viscosity, ν. Although the near-wall streamwise velocity gradient d<U_z>/dy|_y=0 decreases, the larger increase in ν reduces u_z⁺ and leads to the deviation from the law-of-the-wall. Downstream the flame impingement location, ν is relatively constant and u_z⁺ values begin to approach those of the law-of-the-wall. Trends are presented for SWQ and head-on quenching flame topologies, and are intended to help development of more accurate wall models.