Flow-field evolution and vortex structure characteristics of a high-temperature buoyant jet

Abstract

High-temperature buoyant jets generally exist at the exhaust port during the casting process. Canopy hoods are employed to capture these jets in industrial plants. However, because of the lack of flow-field evolution and vortex structure characteristics of the buoyant jets, the optimal design of canopy hood is lack of guidance. In this study, the effects of different initial temperatures (T0) of buoyant jets on the evolution of the temperature, velocity, and vorticity magnitude fields and vortex structure characteristics were studied by large-eddy simulation. The results showed that for 100–1200 °C buoyant jets, the contracted section, which is useful in determining the preferred canopy hood installation position, is generated within 0.7–2 times the source diameter from the nozzle (Z/D). As T0 increases, the position of the contracted section tends to come closer to the nozzle, and the space height for temperature attenuation in the core region is reduced. The contracted section formation results from the rupture of the vortex ring. Because the vortex ring can restrict the diffusion of the buoyant jet, the initial temperature has little effect on the diffusion angle within 4 Z/D. In addition, the spiral vortex structure entrains a large quantity of ambient air, which causes the exhaust flow rate to increase sharply. These conclusions may guide for the design of the exhaust hood installation height for high-temperature buoyant jets to achieve energy savings.