Numerical Investigation of Streamwise Vortex Interaction 2015-01-2573

Streamwise vortices can be observed to interact in a number of real world scenarios. Vortex generators operating in boundary layers, as well as aircraft flying in formation can produce vortex interactions with multiple streamwise vortices in close proximity to each other. The tracking of these vortex paths as well as the location and nature of their breakdown is critical to determining how the structures can be used to aid flow control, and how large scale turbulence develops from them.

Six configurations of two NACA0012 vanes were evaluated computationally to observe the interactions of a pre-existing vortex with a vortex generated downstream. Co and counter-rotating configurations at three different lateral spacings were used to vary vortex position and impingement on the rear vane. RANS testing of all configurations revealed that the strength of the downstream vortex in the co-rotating case was largely unaffected by the presence of the upstream vortex, while the counter-rotating case saw a reduction in vortex strength of up to 30%. LES simulations to better understand the flow mechanisms exhibit the Crow instability in the counter-rotating case and a helical merging pattern in the co-rotating condition.

These findings show that multiple vortex generators can be used to re-energize vortices, allowing far longer vortices than commonly achieved in fields such as flow control. The outcomes indicate that accurate positioning of counter-rotating vortex pairs to cause the premature destruction of undesirable vortices is possible.