Experiments on asymmetric vortex pair interaction with the ground
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RESEARCH ARTICLE
Experiments on asymmetric vortex pair interaction with the ground Qingmin Chen1 · Tianxiang Hu1 · Peiqing Liu1 · Yue Liu2 · Qiulin Qu2 · Hao Guo2 · Rinie A. D. Akkermans3 Received: 5 February 2020 / Revised: 21 May 2020 / Accepted: 26 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The interaction between the asymmetric vortex pair and the ground was experimentally investigated in a closed-circuit water channel for the current study. Particle image velocimetry tests were conducted to achieve the velocity measurements of flow fields at various crossflow planes. The vortex pair, with the reference circulation Reynolds number R eΓ ≈ 4490, was tested with various initial heights (h0/b0 = 1.5, 1.0 and 0.5) and circulation ratios (λ = 0.36:1, 1:0.36, 0.6:1, 1:0.6), with it being found that according to different interaction effects, the trajectory and merger of the vortex pair could be significantly affected. As the primary vortex pair approached the ground, a high turbulent kinetic energy region was observed between the secondary and primary vortical structures, which suggests violent interaction and accelerated circulation decay of the primary vortex. In addition, depending on the distribution of secondary vorticity and image vortices to the moving coordinate system, merging-promoting or -inhibiting effects were observed, which eventually affected the evolution of the primary vortex pair. Graphic abstract
* Tianxiang Hu [email protected] Extended author information available on the last page of the article
List of symbols a Vortex core radius b Vortex separation b0 Initial vortex separation
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c Root chord length dL Distance between γS and VL dR Distance between γS and VR h Height of the primary vortex h0 Initial height of the primary vortex M Number of streamwise locations mi Intersection of the ξ axis and the maximum vorticity line NS Number of γS nj Intersection of the η axis and the maximum vorticity line PIV Particle image velocimetry r Pearson coefficients TKE Normalized turbulent kinetic energy U∞ Free-stream velocity UI Accumulated net induced velocities uI Relative velocity component along the ξ axis induced by γS uIL Induced velocity component on the VL from γS uIL,ξ Magnitude of uIL along the ξ axis uIR Induced velocity component on the VR from γS uIR,ξ Magnitude of uIR along the ξ axis u′y Velocity fluctuation in the direction of the y-axis u′z Velocity fluctuation in the direction of the z-axis VL Primary left vortex VR Primary right vortex x Streamwise coordinate y Lateral (spanwise) coordinate yS Lateral (spanwise) coordinate of γS z Vertical coordinate zL Vertical coordinate of VL zR Vertical coordinate of VR zS Vertical coordinate of γS Γ Circulation of the primary vortex Γ0 Initial primary vortex circulation ΓL Circulation of VL ΓR Circulation of VR Γref Reference circulation γS Arbitrary circulation element of secondary vorticity θL Orientation angles betw
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