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Numerical Investigation of Steady and Harmonic Vortex Generator Jets Flow Separation Control

Department of Mechanical Engineering, Chair of Fluid Mechanics, University of Kassel, 34125 Kassel, Germany
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Fluids 2018, 3(4), 94; https://doi.org/10.3390/fluids3040094
Received: 9 October 2018 / Revised: 28 October 2018 / Accepted: 14 November 2018 / Published: 17 November 2018
Active flow control of canonical laminar separation bubbles by steady and harmonic vortex generator jets (VGJs) was investigated using direct numerical simulations. Both control strategies were found to be effective in controlling the laminar boundary-layer separation. However, the present results indicate that using the same blowing amplitude, harmonic VGJs were more effective and efficient at reducing the separated region than the steady VGJs considering the fact that the harmonic VGJs use less momentum than the steady case. For steady VGJs, longitudinal structures forming immediately downstream of the injection location led to the formation of hairpin-type vortices, causing an earlier transition to turbulence. Symmetric hairpin vortices were shown to develop downstream of the forcing location for the harmonic VGJs, as well. However, the increased control effectiveness for harmonic VGJs’ flow control strategy is attributed to the fact that the shear-layer instability mechanism was exploited. As a result, disturbances introduced by VGJs were strongly amplified, leading to the development of large-scale coherent structures, which are very effective at increasing the momentum exchange, thus limiting the separated region. View Full-Text
Keywords: laminar separation; flow control; vortex generator jets laminar separation; flow control; vortex generator jets
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Alimi, A.; Wünsch, O. Numerical Investigation of Steady and Harmonic Vortex Generator Jets Flow Separation Control. Fluids 2018, 3, 94.

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