Numerical Study Of The Flow Structures On The Strut-hub Juncture

The aeroengine has a large number of struts in its interior.The junction occurs between the strut and the casing.The complex structure of junction flows can result in undesirable effects in practical cases.It is important and meaningful to understand the flow structures and dynamics of junction flows correctly.In order to fully understand the structures at the strut root,the study carried out numerical simulations by using the three-dimensional large eddy simulation?LES?approach.The numerical simulations reproduced the accuracy well by comparison with the experimental results.The velocity field on the symmetry in front of the wing was analysed by the Dynamic Mode Decomposition?DMD?.The result shows that the junction flow which is turbulent is the multiple-frequency phenomena.The paper extracted three main DMD modes,a mean flow mode and two oscillation modes,and the frequencies of the two oscillation modes are66.7Hz and 105.7Hz,respectively.These two extracted DMD modes were reconstituted with the mean flow mode and evolved in time domain to reveal the oscillation characteristic of the horseshoe vortex.The 1^stmode reveals the merging of the horseshoe vortices;the 2^ndmode develops the process of fission and stretching.In order to comprehensively obtain the effect of the angle of attack on the wake of the junction flow,the paper simulated the turbulent flow at the 0°,6°and 12°angle of attack.The time-averaged results were analyzed and the three-dimensional flow structure in the flow field around the airfoil was observed,including the structure of horseshoe vortex,corner vortex and back vortex,etc.The reasons for their formation were analyzed and the interaction between them was also given.The change of the flow structure at the strut root with different angles of attack was discussed.The laminar junction flow was simulated to investigate the horseshoe vortex system.The velocity field on the symmetry in front of the wing was analysed by the Fourier Mode Decomposition?FMD?,and it is found that the flow pattern of the horseshoe vortex is a multi-frequency flow phenomenon.These two extracted DMD modes were reconstituted with the mean flow mode and evolved in time domain to reveal the oscillation characteristic of the main modes.For the 1^st mode,the downstream vortex is stretched and merges into the upstream vortex,forming a new horseshoe vortex.For the 2^ndmode,the upstream vortex merges into the downstream vortex and induces the process of fission.