Characterization of confined swirl flows using Large Eddy Simulations

Since the flame of high intense low NOx gas turbine combustion systems is stabilized by swirl, the analysis of the swirl flow is very crucial to the design and optimization of such combustion systems. Although a huge amount of publications have been provided on this field just a few have used Large Eddy Simulation due to limits in computer resources. Using Large Eddy Simulation the large vortical structure of the flow is resolved leading to a much better insight of the flow features. Hence, in this paper the Large Eddy Simulation has been applied to investigate the non reacting confined swirling flow downstream of a gas turbine burner. A high accuracy of the prediction of the full three dimensional simulation could be pointed out by comparison of the computational results to measurements. Further the large vortical structure and the dynamic behavior of the flow has been analyzed. The formation of a precessing vortex core is visualized. Due to the precessing motion of the central recirculation zone an alternate vortex shedding at the edges of the burner nozzle is induced. From LES Strouhal numbers for the vortex shedding process are calculated which are confirmed by hot wire measurements.