Large coherent structures visualization in a swirl burner

The consumption of fossil fuels and their greenhouse emissions have increased research to develop new mechanisms for the generation of energy and a variety of industrial processes. However, many of the mechanisms under scrutiny have only been measured by indirect simulations. Swirling flows represent this category. Even thought they have been extensively analyzed, there are many uncertainties concerned to their behavior, especially those related to coherent structures and their relationship to the Central Recirculation Zone (CRZ), which is responsible for enhanced mixing and combustion stability. Although extensive programs on the coherent structures generated have been developed, structures such as the Precessing Vortex Core (PVC) and indeed the CRZ remain barely understood. Recent work using numerical simulations (DNS, LES, etc.) have predicted relationships between the PVC and CRZ. The problem lies in the lack of detailed experimental data to validate the results of the interaction, since the measurement has only been done using indirect techniques. Therefore, this paper adopts the approach of producing direct fundamental data on these structures in order to visualize the phenomenon under different conditions. Here the effects of combustion are ignored. Phase Locked Particle Image Velocimetry (PIV) provides results about the interaction of the PVC and CRZ, giving details of shape and dependence on non-dimensional parameters. Various cases were analyzed to find operational regions where strong perturbations occurre d, which lead to the selection of cases that were inspected in detail. 3D holograms were produced in MatLab showing the real spatial interaction of these large structures. Shapes and interactions between different structures are compared and discussed in order to detail the relationship shared between different cases. The most stable and recognizable configuration was analyzed in detail under unconfined and confined conditions. The use of different triggering levels confirmed the accuracy of the technique, with implications of using different signals filters for future projects. No bifurcations or major perturbations were observed during the process, but the appearance of new structures made evident the high correlation between the geometry and type of flow in the burner. The results refuted the normally assumed helical shape of the PVC with a complex spiraling mechanism being revealed. The CRZ was shown in fact to consist of two normally separate, but intertwined CRZs both of which interacted with the PVC.