Flow Structures of Wishbone Vortex Generators and Their Interactions with a Backward-Facing Ramp

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Flow Structures of Wishbone Vortex Generators and Their Interactions with a Backward-Facing Ramp

Cheawchan, A. / Mohamed, M. A. / Ng, B. F. / New, T. H.

In this study, streamwise vortex structures produced by wishbone vortex generators (VGs) and their interactions with a 30° backward-facing ramp (BFR) are investigated to understand their impact upon BFR flow separation behavior at Re⁡=3×106. In particular, the effects of skewing the VGs relative to the free-stream are considered and results compared to those reported for vane-type VGs previously. Near-field formations of and interactions between the primary streamwise, horseshoe, and edge vortices are clarified along with the stagnation points and recirculating regions, where they are sensitive towards the VG skewness angle. Streamwise vortex-core strengths, trajectories, and other characteristics are also quantified. While the formations and behavior of streamwise vortices by wishbone and vane-type VGs imposed on a BFR are generally similar, there exist certain key differences. Comparisons with earlier studies show that vane-type VGs tend to produce far more persistent streamwise vortices with stronger circulation levels, while wishbone VGs tend to produce weaker streamwise vortices that convect slightly closer to the BFR surface. Interestingly, numerical predictions show that multiple streamwise vortices produced by a wishbone VG array interact more significantly than its vane-type counterpart even at a small skewness angle of 10°. This leads to much larger reattachment length reductions along the BFR span and potentially offers considerable pressure drag reduction levels.