Geometrical Analysis of Hairpin Vortices in Turbulent Channel Flow

Hairpin vortices are key coherent structures in wall-bounded turbulence and play an important role in momentum transport and the spatial organization of turbulent motions. Despite extensive qualitative investigations, their quantitative geometric characteristics and wall-normal evolution in turbulent channel flows remain incompletely documented. This study presents a concise geometrical and statistical analysis of hairpin vortices extracted from a turbulent channel flow at friction Reynolds number Re = ۱۸۰. A total of ۴۴ hairpin vortices, identified using a multi-method detection framework, are analyzed under the assumption of fully developed channel turbulence. The analysis focuses on vortex height, spanwise width, streamwise length, aspect ratio, and volume, together with the wall-normal distribution of vortex centroids. Statistical behavior is quantified using probability density and cumulative distribution functions, and variations of geometric properties are examined as functions of centroid wall-normal location. The results show that hairpin vortices are predominantly concentrated within the buffer and logarithmic layers. With increasing wall-normal distance, vortices exhibit progressive streamwise elongation, while their height, spanwise width, and volume systematically decrease. These trends indicate increasing geometric anisotropy and reduced coherence away from the wall. The reported statistics provide a compact quantitative description of hairpin vortex geometry and offer reference data for studies of coherent structures in turbulent channel flows at comparable Reynolds numbers.

کلیدواژه ها:

Hairpin vortices ، Turbulent channel flow ، Coherent structures ، Geometrical statistics