Identifying and tracking surface-attached vortices in free-surface turbulence from above: a simple computer vision method
- 1Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway (omer.babiker@ntnu.no)
- 2Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway (ivarbje@stud.ntnu.no)
- 3Department of Mechanical Engineering and Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis, USA (shen@umn.edu)
Turbulence close beneath a free surface leaves recognisable imprints on the surface itself. The ability to identify and quantify long-lived coherent turbulent features from their surface manifestations only could open up possibilities for remote sensing of the near-surface turbulent environment, e.g., for assimilation into ocean models. Our work concerns automatic detection of one type of surface feature – “dimples” in the surface due to surface-attached “bathtub” vortices – based solely on the surface elevation as a function of time and space.
Two-dimensional continuous wavelet transformations are used together with criteria for eccentricity and persistence in time, to identify candidate surface-attached vortices and track their motion. We develop and test the method from direct numerical simulation (DNS) data of turbulence influenced – and influencing – a fully nonlinear, deformable free surface.
Comparison with the vertical vorticity in a plane close beneath the surface reveals that the method is able to identify long-lived vortical structures with a high degree of accuracy. Further tests of success rate included the vortex core identification method of Jeong and Hussain (1995). Different mother wavelets were tested, showing that the simplest option – the Mexican hat – outperforms more advanced options.
Jeong, J., & Hussain, F. (1995). On the identification of a vortex. Journal of fluid mechanics, 285 69-94.
How to cite: Babiker, O., Bjerkebæk, I., Xuan, A., Shen, L., and Ellingsen, S. Å.: Identifying and tracking surface-attached vortices in free-surface turbulence from above: a simple computer vision method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9776, https://doi.org/10.5194/egusphere-egu22-9776, 2022.
