Drag force on an accelerating submerged plate
| Autor: | N. B. Vijayaragavan, Mark J. Tummers, Jerry Westerweel, Ernst Jan Grift |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: |
Materials science
Mechanical Engineering Applied Mathematics Reynolds number 02 engineering and technology Mechanics Wake 021001 nanoscience & nanotechnology Condensed Matter Physics Vortex shedding 01 natural sciences wakes 010305 fluids & plasmas Morison equation Vortex Physics::Fluid Dynamics symbols.namesake Acceleration Particle image velocimetry Mechanics of Materials Drag 0103 physical sciences symbols vortex shedding 0210 nano-technology |
| Zdroj: | Journal of Fluid Mechanics, 866 |
| ISSN: | 0022-1120 |
| Popis: | 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$AR=2$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$4\times 10^{4}\lesssim Re\lesssim 8\times 10^{4}$. 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$1/5$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 Gharibet 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. |
| Databáze: | OpenAIRE |
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