Dynamics of multiple swirling burner flows

Abstract

Numerical predictions of four counter and co-rotating swirling flows issuing from small-scale low NOx burners have been performed and compared to laser Doppler anemometry (LDA) measurements. The results demonstrate that the near-burner features, such as the central reverse flow zones and the mixing of the burner jets, are resolved correctly by the computational model. Predicted tangential velocity components are in good agreement with the LDA measurements, and show the correct swirl velocity profiles and rate of decay. The anti-gearing phenomenon associated with the entrainment pattern of the counter and co-rotating burner arrays, where flow is entrained into the centre of the array against the direction of swirl, is captured by the LDA measurements and is predicted by the CFD model. Predicted rates of entrainment of surrounding air by the counter and co-rotating burners intimate that a counter-rotating burner array entrains at a greater rate than a single burner. A co-rotating system, however, entrains at a lower rate. The ability to control levels of entrainment may provide the means of further controlling air staging in real furnaces. The research demonstrates that multi-burner systems may be characterised in terms of the number of burners, their rotational direction, the burner pitch and the degree of entrainment.