The effect of sweep on a transitional separation bubble behind a backward-facing step is investigated using direct numerical simulation (DNS). The Reynolds number based on step height and free stream component normal to the step, Re(α)=(HC(∞) cos α)/υ, is kept constant at 3000 for sweep angles α between 0°and 60°. Results agree well with two experimental investigations. Up to α=40°, the mean flow follows the sweep-independence principle. For higher sweep angles, the size of the separated flow region is shortened considerably which is mainly due to an upstream shift of transition in the laminar shear layer emanating from the step and-to a lesser degree-to an increase in turbulent momentum flux uῡ. Fluctuations of wall-stress and wall pressure are largest near the reattachment location and their magnitude scales with (C(∞) cos α)2 for all sweep angles. Transition is dominated by a Kelvin-Helmholtz-type instability of the free shear layer. The influence of skewing on the growth rate of instability waves is weak in accordance with linear stability theory predictions of Lu and Lele [J. Fluid Mech. 249, 441 (1993)]. The upstream shift of transition for α≥50°is related to the way how disturbances spread sidewise in a wedge-shaped region inside of the shear layer. (C) 2000 American Institute of Physics. A 3D extension of a well-known 2D flow was investigated. The goal of study is to identify the influence of sweep on the separated flow behind the step edge. A series of direct numerical simulations were carried out. The transition process depends on the way how disturbances enter the laminar shear layer and the size of the separated flow region is found to be very sensitive with respect to magnitude and frequency content of background disturbances superimposed to the flow.     «

The effect of sweep on a transitional separation bubble behind a backward-facing step is investigated using direct numerical simulation (DNS). The Reynolds number based on step height and free stream component normal to the step, Re(α)=(HC(∞) cos α)/υ, is kept constant at 3000 for sweep angles α between 0°and 60°. Results agree well with two experimental investigations. Up to α=40°, the mean flow follows the sweep-independence principle. For higher sweep angles, the size of the separated flow re...     »