Visualisation of Turbulent Flows in a Swirl Burner under the effects of Axial Air Jets

Abstract

Meeting emission regulations represents a real challenge in the power generation sector. Swirl combustors and their operation under lean premixed (LP) conditions are a step towards attaining low emissions, especially NOx formation, while ensuring high efficiency. However, performing modifications on combustors and reaching the requirements of efficient combustion systems is difficult due to many combustion problems such as extinction, low reaction rates, mild heat release, instabilities, and mixing issues. Thus, giving careful attention to the hydrodynamics design of the swirl burners with extensive testing methods in both experimental and numerical approaches is crucial to stabilise the combustion phenomena in gas turbines. As a result, this study employed the implementation of CFD simulations in the design of a 150 kW tangential swirl burner and considered the consequences of 50 LPM diffusive air injection at different positions on three-dimensional isothermal flow field characterizations, especially the turbulence, downstream the burner nozzle. Various mass flow rates from 600 to 1000 l/min were used at atmospheric conditions with a geometrical swirl number of 0.913. Experimental work was conducted with good correlation. It was found that using the air injection system could increase the flashback resistance by affecting the velocity defect downstream the burner nozzle. Moreover, the axial air jet reduces the flow field turbulence at the central recirculation zone (CRZ) tip and hence minimises the flow fluctuations and affect its size and position. CFD results show a very good agreement with Laser Doppler Anemometry (LDA) data acquired from the experimental work.