Swirling and Impinging Effects in an Annular Nonpremixed Jet Flame

Abstract

The effects of swirl and downstream wall confinement on an annular nonpremixed flame were investigated using direct numerical simulation (DNS). Fully three-dimensional parallel DNS was performed employing high-order numerical methods and high-fidelity boundary conditions to solve governing equations for variable-density flow and finite-rate Arrhenius chemistry. Three swirl numbers have been examined: 0 (without swirl), 0.4 and 0.8, while the effects of downstream wall confinement have been examined for swirl numbers 0 and 0.4. Results have been presented in terms of instantaneous and time-averaged flow quantities, which have also been analysed using energy spectra and proper orthogonal decomposition (POD). Effects of swirl on the fluid dynamic behaviour of the annular nonpremixed flame were found to be significant. The fluid dynamic behaviour of the flame is greatly affected by the interaction between the geometrical recirculation zone (GRZ) near the jet nozzle exit due to the annular configuration, the central recirculation zone (CRZ) associated with swirl, the unsteady vortical structures in the jet column due to the shear instability, and the downstream wall confinement. Depending on the degree of swirl, the GRZ near the burner mouth and the CRZ may co-exist or one zone may be overwhelmed by another. At a moderate swirl number, the co-existence leads to a flame with strong reaction attached to the burner mouth; while at a high swirl number, the CRZ dominates over the GRZ. The precessing vortex core was 64 Flow Turbulence Combust (2011) 86:63-88 observed to exist in the swirling flow fields. The Nusselt number distribution of the annular impinging flames differs from that of round impinging jets. The POD analysis revealed that wall effects on the flow field are mainly associated with the higher mode numbers.

Large eddy simulation of impinging flames: Unsteady ignition and flame propagation

“…Impinging flames are also found in combustion engines, by design and/or by accident, which have a major effect on combustion characteristics, heat transfer and emissions. As impinging flames have very different characteristics from those of the widely investigated free jet flames, the study of impinging flames is of fundamental interest to the research communities on heat transfer [1,2], fluid mechanics and combustion [3,4,5,6]. A large number of parameters are involved in impinging flames, which adds to the complexity of the problem.…”

Numerical investigation of the burning characteristics of ventilation air methane in a combustion based mitigation system

“…This configuration permits the investigation of the ignition of the VAM at the boundary of the established jet flame and the subsequent oxidation of the VAM stream. This is considered a preliminary test for more sophisticated and appropriate configurations such as annular burners with swirling effects that improve the mixing and combustion [36,37].…”

Experimental investigation of transient ignition dynamics of hydrogen enriched methane diffusion impinging flames

“…Due to the complex flame-towall interactions, the ignition characteristics of impinging flames have very different features from those of the widely investigated free jet flames [12]. The flame establishment under impinging conditions can be affected by multi factors, including jet flow condition, nozzle to wall distance, ignition initiation position as well as fuel compositions [13][14][15][16]. Wang et al investigated the ignition process of a diffusion propane and a methane impinging flame using high speed colour and schlieren imaging techniques [17,18], respectively.…”