Print Email Facebook Twitter Drag force on an accelerating submerged plate Title Drag force on an accelerating submerged plate Author Grift, E.J. (TU Delft Fluid Mechanics) Vijayaragavan, N. B. (Student TU Delft) Tummers, M.J. (TU Delft Fluid Mechanics) Westerweel, J. (TU Delft Fluid Mechanics) Date 2019 Abstract We present results on the drag on, and the flow field around, a submerged rectangular normal flat plate, which is uniformly accelerated to a constant target velocity along a straight path. The plate aspect ratio is chosen to be to resemble an oar blade in (competitive) rowing, the sport which inspired this study. The plate depth, i.e. the distance from the top of the plate to the air-water interface, the plate acceleration and the plate target velocity are varied, resulting in a plate width based Reynolds number of . In our analysis we distinguish three phases; (i) the acceleration phase during which the plate drag is enhanced, (ii) the transition phase during which the plate drag decreases to a constant steady value upon which (iii) the steady phase is reached. The plate drag force is measured as function of time which showed that the steady-phase plate drag at a depth of plate height (20 mm depth for a plate height of 100 mm) increased by 45 % compared to the plate top at the surface (0 mm). Also, it is shown that the drag force during acceleration of the plate increases over time and is not captured by a single added mass coefficient for prolonged accelerations. Instead, an entrainment rate is defined that captures this behaviour. The formation of starting vortices and the wake development during the time of acceleration and transition towards a steady wake are studied using hydrogen bubble flow visualisations and particle image velocimetry. The formation time, as proposed by Gharib et al. (J. Fluid Mech., vol. 360, 1998, pp. 121-140), appears to be a universal time scale for the vortex formation during the transition phase. Subject vortex sheddingwakes To reference this document use: http://resolver.tudelft.nl/uuid:d33345f3-7252-486b-87f2-f124397330e5 DOI https://doi.org/10.1017/jfm.2019.102 ISSN 0022-1120 Source Journal of Fluid Mechanics, 866, 369-398 Part of collection Institutional Repository Document type journal article Rights © 2019 E.J. Grift, N. B. Vijayaragavan, M.J. Tummers, J. Westerweel Files PDF drag_force_on_an_accelera ... _plate.pdf 2.82 MB Close viewer /islandora/object/uuid:d33345f3-7252-486b-87f2-f124397330e5/datastream/OBJ/view