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Abstract
The successful control of vortex structures is critical in the field of modern aerodynamics, with automotive and aerospace applications becoming increasingly reliant on vortices to improve aerodynamic efficiency. Knowledge of how streamwise vortex interactions behave as they propagate downstream is essential to designing systems to control these flow structures.
The flow around two NACA0012 vanes at various lateral offsets was investigated by a combination of experimental and numerical means to observe the interactions between two streamwise vortices. The vanes were separated in the streamwise direction, allowing the upstream vortex to impact on the downstream geometry. Initial investigations were performed using water tunnel dye visualisation and Reynolds-Averaged Navier-Stokes analysis, with more detailed Large Eddy Simulations and Particle Image Velocimetry used for quantitative assessment of vortex energies and paths.
Circulation enhancement of the upstream vortex occurred at all offsets for the co-rotating case. The counter-rotating condition was considerably more sensitive to offset, with far offsets causing vortex enhancement and near offsets causing vortex destruction. The presence of the upstream vortex was found to increase the production strength of the downstream vortex in the counter-rotating condition, and decrease it in the co-rotating condition. However, the counter rotating condition was found to have more rapid energy loss than the co-rotating condition, which did not significantly lose circulation across the domain.
In all co-rotating conditions the vortices were seen to tend to an asymmetric merger, however the merging distance was found to be chaotic rather than static. Meandering was found to occur in both vortices of the co-rotating pair, with the downstream vortex experiencing a faster growth rate and the oscillations equalising between the vortices. The oscillation was determined to be responsible for the variation in merging location, with variation in vortex separation causing the state at a single plane to merge and unmerge. In the counter-rotating condition oscillations were found to be larger, with higher growth, but less uniform periodicity.
Ultimately it was found that, under certain circumstances, interaction with a counter-rotating downstream vortex could successfully destroy an existing upstream vortex, while a co-rotating downstream vortex would re-energise the existing vortex in all conditions.