Trailing wake vortices: Experimental and modeling comparisons

Abstract

Available literature has demonstrated a scarcity of data collected behind simple, academic wings that were not NACA profiles. Additionally, comparison of the simplified vortex models is typically performed piecewise without a broad comparison between models. In the present investigation, the structure of an isolated wake vortex is studied and a more thorough comparison of wake vortex models is performed. Experimental data is presented that primarily focuses on the vortex generated by a flat-plate wing. Additional data for a NACA 0015 wing of similar aspect ratio is investigated to validate the experimental method. The experimental method presented utilizes a linear two-axis traverse to position a conventional seven-hole probe in the wake of the generating wing. A semi-span model is used to generate the vortex. Twenty-two vortex surveys are presented between four and sixteen chord lengths downstream of the trailing edge of the generating wing. Vortex core circulation ranges from 8 × 104 to 66 × 104. Vortices presented exhibit a faster decay in peak tangential velocity than reported in some experimental data, but circulation within the core region is shown to remain constant. Comparisons of the current experimental data and simplified models suggests that both the flat plate and NACA 0015 models produce a turbulent vortex. Evidence is presented that suggests that vortex circulation is not the only governing factor on whether a vortex exhibits a laminar or turbulent profile. Fourteen axisymmetric vortex models are considered and their circulation, tangential velocity, and vorticity distributions compared. Both laminar and turbulent models are considered. Discussion is presented on the relationship of vortex circulation and the transition from a laminar to turbulent character. Comparisons highlight a common trend of increased tangential velocity in turbulent vortices at larger radii for the same vortex strengths. Some models estimate unbounded circulation, particularly among turbulent formulations.