Evolution of vortex structure around a wall-mounted rough hemisphere

In this paper, the large eddy simulation (LES) method is used to calculate Reynolds numbers the range in the range of 3 000-30 000 (based on the diameter of the hemisphere D), and then the statistical analysis method is used to study the influence of Re on the characteristics of the flow field around the rough hemisphere and the evolution law of the tail vortex. The effect of the Reynolds number on the structure of the rough hemisphere flow field and the evolution of vortex structure is studied by vorticity distribution, POD method, and correlation analysis. It can be observed that with the increase of Reynolds number, the shear in the recirculating region of the rough hemisphere is enhanced, the large-scale structure is reduced, the small-scale structure is increased, and the angle between the hairpin vortex and the wall is reduced. & lambda;(ci) vortex identification and the Q-criterion are used to capture the evolution of a periodic vortex structure. Q-criterion gives the three-dimensional vortex structure behind the hemispherical flow. It is found that the horseshoe vortex and arch vortex generated by the incoming flow after passing through the hemisphere will interact with the wall surface to form a hairpin vortex, and the hairpin vortex structure will continue to evolve downstream to form a new vortex structure.