Abstract
The oblique interaction of a turbulent vortex ring with a clean water surface is experimentally investigated during the transition stage using Digital Particle Image Velocimetry (DPIV) and the shadowgraph technique to map the surface velocity and deformation field simultaneously. The transitional vortex-ring/free-surface interaction leads to the formation of a trifurcation pattern at the free surface. Similar to the laminar flow case, the vortex ring initially bifurcates into two symmetric and separately connected vortex loops. The turbulent break-up of those vortex loops results in the formation of longitudinal wake vortices that symmetrically connect to the surface and eventually lead to a trifurcation pattern. In the absence of large-deformation surface waves, the simultaneous DPIV and shadowgraph measurements reveal good agreement between the surface vorticity and deformation field for small- and large-scale vortical structures. The simultaneous measurement technique is not restricted to the qualitative shadowgraph visualization, but can be easily extended to quantitative methods such as grating-imaging techniques, Color Schlieren, or Color Surface Mapping (CSM) techniques.
Similar content being viewed by others
References
Bernal LP; Kwon JT (1989) Vortex ring dynamics at a free surface. Phys Fluids A 1: 449–451
Bernal LP; Hirsa A; Kwon JT; Willmarth WW (1989) On the interaction of vortex rings and pairs with a free surface for varying amounts of surface active agents. Phys Fluids A 1: 2001–2004
Berry MV; Hajnal JV (1983) The shadows of floating objects and dissipating vortices. Optica Acta 30: 23–40
Dommenmuth DG (1994) The initialization of vortical free-surface flows. J Fluids Eng 116: 95–102
Gharib M; Weigand A; Willert C; Liepmann D (1992) Experimental studies of vortex reconnection to a free surface: A physical flow model. Proc. 19th Symp. Naval Hydrodynamics, Seoul, Korea: 189–201
Krutzsch CH (1936) Über ein instabiles Gebiet bei Wirbelringen. Z Ang Math Mech 16: 352–353
Krutzsch CH (1939) Über eine experimentell beobachtete Erscheinung an Wirbelringen bei ihrer translatorischen Bewegung in wirklichen Flüssigkeiten. Ann Physik 35: 497–523
Kurata J; Grattan KTV; Uchiyama H; Tanaka T (1990) Water surface measurement in a shallow channel using the transmitted image of a grating. Rev Sci Instr 61: 736–739
Kwon JT (1989) Experimental study of vortex ring interaction with a free surface. Technical Report No. 89–06, University of Michigan, Department of Aerospace Engineering, Ann Arbor, MI
Sarpkaya T (1992) Three-dimensional interactions of vortices with a free surface. AIAA Paper 92-0059
Sarpkaya T; Magee M; Merrill C (1994) Vortices, free-surface and turbulence. In: Free Surface Turbulence, Rood EP, Katz J (Eds) FED-Vol. 181: 1–14
Sterling MH; Gorman M; Widman PJ; Coffman SC; Strozier J; Kiehn RM (1987) Why are these disks dark? The optics of Rankine vortices. Phys Fluids 30: 3624–3626
Weigand A; Gharib M (1994a) On the decay of a turbulent vortex ring. Phys Fluids 16: 3806–3808
Weigand A; Gharib M (1994b) Turbulent vortex-ring/free-surface interaction. In: Free Surface Turbulence, Rood EP, Katz J (Eds). FED-Vol. 181: 59–67 and accepted for publication in J Fluids Eng
Widnall SE; Sullivan JP (1973) On the stability of vortex rings. Proc Roy Soc Lond A 332: 335–353
Widnall SE; Bliss DB; Tsai CY (1974) The instability of short waves on a vortex ring. J Fluid Mech 66: 35–47
Willert CE; Gharib M (1991) Digital particle image velocimetry. Exp Fluids 10: 181–193
Zhang X; Cox ChS (1994) Measuring the two dimensional structure of a wavy water surface optically: A surface gradient detector. Exp Fluids 17: 225–237
Author information
Authors and Affiliations
Additional information
This work has been supported by the Office of Naval Research, ONR-URI grant N00014-92-J-1610.
Rights and permissions
About this article
Cite this article
Weigand, A. Simultaneous mapping of the velocity and deformation field at a free surface. Experiments in Fluids 20, 358–364 (1996). https://doi.org/10.1007/BF00191017
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00191017