The variation in Co and counter-rotating upstream-downstream vortex interactions

The interactions between two streamwise vortices at various lateral offsets were investigated by the wind tunnel testing of two NACA0012 vanes. The vanes were separated by nine chord lengths in the streamwise direction such that the upstream vortex impacted on the downstream geometry. These vanes were evaluated at an angle of incidence of 8 degrees and a Reynolds number of 70,000, with Particle Image Velocimetry (PIV) used for data collection. To produce a co-rotating pair, both vane angles were orientated in the same direction, while to produce a counter-rotating pair the angle of the rear vane was reversed. Despite the fundamental similarity of the flow field in terms of the presence and proximity of two vortices, pronounced differences were observed in both the vortex paths and the energy transfer between the two vortices. Circulation enhancement of the upstream vortex occurred at all lateral offsets for the co-rotating case. The counter-rotating condition was far 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 observed.