Flame speed characteristics of turbulent expanding flames in a rectangular channel

We present results from studies of freely expanding flames in a unique small-scale convective facility for different free-stream initial conditions, characterized by Taylor-Reynolds numbers in the range of Re-lambda g = 179 395 (using the streamwise RMS velocity component and the lateral Taylor-microscale) and an inertial subrange over two decades of wavenumbers. The isotropic, decaying turbulence is generated by an active vane grid. Adding natural gas far upstream, the premixed flow is ignited using Laser Induced Breakdown (LIB) ignition. The evolution of the resulting spherically expanding flames is investigated using qualitative OH-Planar Laser Induced Fluorescence (PLIF). It is shown that trends of flame speeds derived from mean flame radius growth agree well with results from different experimental setups, using a recently developed scaling based on a spectral closure of a thin flame model (Chaudhuri et al., Phys. Rev. E (2011)). Reliable computation of the flame surface density and turbulent flame brush thickness is enabled by the large number of ensembles that can be collected in this type of facility. Trends of these instantaneous statistical quantities are presented and used to further assess the results of time-dependent mean quantities. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.