Effect of spanwise extension on the wake dynamics of flow around a wall-mounted prism

The effect of spanwise extension on the wake dynamics of flow past a wall-mounted prism is investigated using direct numerical simulations at Reynolds numbers

,

500 500 $500$

and

1000 1000 $1000$

and spanwise extents

b divided by h equals 1 b / h = 1 $b/h=1$

,

3 3 $3$

and

5 5 $5$

. A horseshoe vortex (HsV) system forms upstream of the prism in all cases, while in most flows the leading-edge shear layer undergoes Kelvin–Helmholtz (KH) instability, generating KH vortices that evolve into arch-shaped vortices (ArcV) and subsequently hairpin vortices (HV). As

italic Re Subscript h Re h $\textit{Re}_h$

and

b divided by h b / h $b/h$

increase, the wake exhibits increasingly complex vortex dynamics. At

italic Re Subscript h Baseline equals 300 Re h = 300 $\textit{Re}_h=300$

, the HsV system remains stable. For

b divided by h equals 5 b / h = 5 $b/h=5$

, the downstream wake exhibits a subharmonic associated with periodic alternation between two ArcV-to-HV evolution modes. At

italic Re Subscript h Baseline equals 500 Re h = 500 $\textit{Re}_h=500$

, dual vortex-evolution modes persist for

b divided by h equals 3 b / h = 3 $b/h=3$

and

5 5 $5$

, accompanied by dual shedding frequencies. At

italic Re Subscript h Baseline equals 1000 Re h = 1000 $\textit{Re}_h=1000$

, the HsV system becomes unstable for

b divided by h equals 3 b / h = 3 $b/h=3$

and

5 5 $5$

, generating streamwise-elongated braid vortices whose passage coincides with earlier destabilisation of the leading-edge shear layer. For

b divided by h equals 3 b / h = 3 $b/h=3$

, the unstable HsV system exhibits two characteristic frequencies associated with coherent system-wide vortex dynamics. For

b divided by h equals 1 b / h = 1 $b/h=1$

, the wake exhibits dual-frequency KH dynamics and develops a dual-row side-HV. Spanwise extension significantly enhances wake fluctuations. The turbulent kinetic energy is concentrated in regions of HV and side-HV formation, and is dominated by the streamwise component, with energy subsequently redistributed towards the vertical and spanwise components.