Flow-following behavior of centimeter-sized air-filled soap bubbles as assessed in a cylinder wake
S. Brückner(1), R. Leister(2), M. Hilfer(1), D.E. Rival(1,3)
1: Institute of Fluid Mechanics, TU Braunschweig, Germany
2: Institute for Modelling Hydraulic and Environmental Systems, University of Stuttgart, Germany
3: Department of Mechanical Engineering, Queen’s University, Canada
DOI:
In this study, the flow-following behavior of centimeter-sized air-filled soap bubbles is explored in the wake of a circular cylinder in order to assess when these soap bubbles no longer faithfully follow the flow. Air-filled soap bubble motion is captured by tracking the two largest glare points, with depth retrieval based on the glare-point particle tracking technique. The experiments are conducted in the wake of a circular cylinder at a freestream velocity of U∞ ≈ 6 m s−1 . Based on the cylinder diameter, this corresponds to a Reynolds number of ReD ≈ 65000. To assess the flow-following behavior, a dimensionless time-scale ratio η = τp /τf is introduced. The distribution of η shows that, for 10.4% of all wake sample points, the particle time scale is smaller than or comparable to the selected wakeflow time scale. When only sample points corresponding to vortical wake tracks are considered, this fraction increases to 28.7%. Key findings • The flow-following behavior of centimeter-sized air-filled soap bubbles is explored in the wake of a circular cylinder in order to assess when these soap bubbles no longer faithfully follow the flow. • To assess the flow-following behavior, a dimensionless time-scale ratio η = τp /τf is intro duced.
