Turbulent flow over a swept backward-facing step

The spanwise invariant flow over a swept, backward-facing step of height H at Re_H=C₀H/ν=5000 with turbulent upstream conditions has been studied for sweep angles up to α=70° using large-eddy simulation. The reattachment length x_R≈6.2 H remains nearly constant up to α=30°, decreases for larger sweep angles, and reaches x_R≈4.0 H for α=70°. Step-normal components U/(C ₀cosα) and edge-parallel components W/(C₀sinα) of the mean flow show approximate collapse for α≤50° if compared at the same location x/x_R. However, the sweep-independence principle does not hold in a strict sense since the scaling of the momentum budgets undergoes significant changes with streamwise distance from the step. Dynamics in the first half of the separation region are strongly influenced by the scaling relations imposed by the upstream conditions. In accordance with the momentum integral theorem the overall pressure rise scales as (C ₀cosα)² which partially explains why several quantities tend to scale near reattachment as if the flow were sweep independent. No significant influence of the mean flow skewing on the statistical turbulence structure is observed inside the free shear layer emanating from the edge. Conversely, introduction of sweep causes substantial changes in the dynamics of the near-wall region upstream of reattachment.