A lifted H2/N2 turbulent jet flame issuing into a vitiated coflow is investigated using the conditional moment closure. The\nconditional velocity (CV) and the conditional scalar dissipation rate (CSDR) submodels are chosen such that they are fully\nconsistent with the moments of the presumed ? probability density function (PDF). The CV is modelled using the PDF-gradient\ndiffusionmodel. Two CSDR submodels based on the double integration of the homogeneous and inhomogeneous mixture fraction\nPDF transport equations are implemented. The effect of CSDR modelling is investigated over a range of coflow temperatures (Tc)\nand the stabilisationmechanism is determined fromthe analysis of the transport budgets and the history of radical build-up ahead\nof the stabilisation height. For all Tc, the balance between chemistry, axial convection, and micromixing, and the absence of axial\ndiffusion upstreamof the stabilisation height indicate that the flame is stabilized by autoignition.This conclusion is confirmed from\nthe rapid build-up ofHO2 ahead ofH,O, andOH.The inhomogeneous CSDRmodelling yields higher dissipation levels at themost\nreactive mixture fraction, which results in longer ignition delays and larger liftoff heights. The effect of the spurious sources arising\nfrom homogeneous modelling is found to be small but nonnegligible, mostly notably within the flame zone.
Loading....