A numerical investigation on flow past skewed vortex generators ahead of a backward facing ramp

Flow past a backward facing ramp (BFR) with rectangular vane-type vortex generators (VGs) located upstream has been studied numerically using OpenFOAM based steady-state RANS simulations. In particular, single and multiple pair(s) of boundary layer height VGs are skewed at 10 and 30 to study their effects on the flow separation behaviour at Re = 3 x 10(6). Streamwise and cross-stream results show that single VGs produce counter-rotating streamwise vortices with increasingly different vortex-core strengths and vortical interactions when skewness angle increases. At 30 however, co-rotating vortices are formed instead with significantly heightened vortical interaction levels, leading to asymmetric flow separation and reattachment behaviour. In particular, the use of multiple VGs under the same condition further accentuate these behaviour and results in significant changes to the wall shear stress distribution. Clarifications on how the flow separation region is distorted by the symmetric/asymmetric streamwise vortices based on velocity component analysis are also provided. Lastly, trajectories of the streamwise vortices and vortex-core characteristics support the notion that the streamwise vortices behave significantly more non-linearly at 30 skewness angle here, and that skewing the present VGs such that they produce co-rotating vortices instead of counter-rotating ones leads to very different flow separation control characteristics. (c) 2022 Elsevier Masson SAS. All rights reserved.

Automated summary

The flow past a backward facing ramp (BFR) with rectangular vane-type vortex generators (VGs) located upstream has been investigated numerically. The effects of single and multiple VGs with different skew angles on flow separation behavior were studied. The results show that single VGs generate counter-rotating streamwise vortices, while multiple VGs under the same condition intensify this behavior and lead to significant changes in the distribution of wall shear stress. The distortion of the flow separation region by symmetric/asymmetric streamwise vortices is clarified based on velocity component analysis. The trajectories and characteristics of the streamwise vortices support the idea that they behave significantly more non-linearly at a skew angle of 30° and that different types of vortices result in distinct flow separation control characteristics.