Ostmann, S., Chaves, H. & Bruecker, C. (2017). Path instabilities of light particles rising in a liquid with background rotation. Journal of Fluids and Structures, 70, pp. 403-416.
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The present paper reports on experimental observations performed on 2–6 mm low-density polystyrene particles rising freely in a water-glycerol mixture for the liquid at rest as well as with slow background rotation (axisymmetric solid body rotation around the vertical axis). Particle trajectories were studied in the Reynolds-numbers range of 200<Re<800 at a fixed rotation rate of Ω=0.81/s. Both the trajectory measurements and the wake visualization indicate that there are differences in the wake structure of the particles as well as in the path instabilities compared to those in quiescent fluid. In the swirling flow, the two-threaded wake mode is dominant up to Reynolds numbers of about 500 with typical spiral-type trajectories until vortex shedding commences. In contrast, under quiescent flow conditions vortex shedding already occurs above Re=230, and the particles predominantly move in zig-zagging paths. Thus, the presence of background rotation is able to suppress vortex shedding and to delay the transition. For the co-rotating observer, the radius of the spiral-type path is comparable to that of the transversal motion under quiescent flow conditions. Therefore, the magnitude of lateral lift-forces is not greatly affected by the presence of the swirl.
|Subjects:||T Technology > TL Motor vehicles. Aeronautics. Astronautics|
|Divisions:||School of Engineering & Mathematical Sciences > Engineering|
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