ACTA AERONAUTICAET ASTRONAUTICA SINICA >
Coherent Structures of Flow Fields in Swirling Flow Around a Bluff-body Using Large Eddy Simulation
Received date: 2013-10-22
Revised date: 2014-01-27
Online published: 2014-02-21
Supported by
National Natural Science Foundation of China (51176178)
Large eddy simulation (LES) is performed to study the non-reacting flow fields of a stratified swirl burner with a central bluff-body. A dynamic Smagorinsky sub-grid scale eddy viscosity model is used. Large scale coherent structures are investigated in the flow fields with a swirling number of 0.45. The results show that the inner and outer helical vortices and precessing vortex core (PVC), displayed by the iso-surface of instantaneous pressure, are orthogonal to the streamlines of mean velocity. This fact supports the idea that the helical vortex and PVC are generated by the Kelvin-Helmholtz shear layer instability. The helical vortex structures, visualized by the iso-surface of Q-criterion, begin to break down at about 20 mm downstream of the burner exit. PVC originates from the downstream shear layer between the annular swirl and jet flow. The power spectral density (PSD) of instantaneous circumferential velocity exhibits an obvious characteristic peak which indicates that PVC leads to the precession motion of the adjacent flow fields. Fluctuating velocity fields are reconstructed using a proper orthogonal decomposition (POD) method. The PSD results of different modes indicate that large scale vortex structures of the first two modes are related to the precession motion. Large scale vortex structures around the PVC can also be clearly visualized by the iso-surfaces of circumferential velocity fluctuations in the first two modes.
ZHANG Hongda , ZHANG Jimin , HAN Chao , YE Taohong . Coherent Structures of Flow Fields in Swirling Flow Around a Bluff-body Using Large Eddy Simulation[J]. ACTA AERONAUTICAET ASTRONAUTICA SINICA, 2014 , 35(7) : 1854 -1864 . DOI: 10.7527/S1000-6893.2013.0535
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