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Flow structures around a wavy square cylinder with a perturbation wavelength of 5.6D are investigated using large eddy simulation at the Reynolds number of 23 500. The detailed force characteristics and wake flow structures of the wavy square cylinder are captured and compared with a square cylinder. Under the effect of wavy leading edge up to 27% and 98% reduction in the mean drag and the lift fluctuations are achieved, respectively. The 3D mean flow field implies a high shear flow between node and saddle positions, which is associated with the generation of additional streamwise and vertical vortex pairs. These vortex structures are responsible for the three-dimensionality of the wake flow behind the wavy square cylinder. The instantaneous flow patterns suggest that the staggered pattern of von Kármán vortex shedding is suppressed and replaced by symmetric vortex shedding into the near wake region of the wavy square cylinder. This symmetric vortex structure in the near wake plays a role in preventing the upper and lower shear layers from interacting with each other. The time–frequency analysis exhibits a reduction in the dominating vortex shedding frequency for the case of wavy square cylinder, indicating a relatively steady wake flow. This can be attributed to the vortex dislocation behind the wavy square cylinder. In the range of high frequencies, small streaks associated with small-scale fluctuations are enhanced by the wavy leading edge. The present study suggests that the perturbation wavelength obtained from the wavelength of Mode A instability at laminar flow regime can be served as a basis for flow control in turbulent flow regime. [ABSTRACT FROM AUTHOR]

In this study, the interaction between a spherical solid particle descending in a fine-bubble plume and the fine-bubbles around the particle is investigated experimentally. The fine-bubbles, which are formed by water electrolysis and have an average diameter of 0.037 mm, rise via buoyancy to form bubble plumes. The average bubble velocity in the conduit is 0.05 mm/s. A spherical solid particle with a diameter of 11.1 mm and a density of 1130 kg/m3 is dropped into the fully-developed bubble plume. The particle falls in a meandering motion in the fine-bubble plume. In this process, the terminal velocity of the particles falling in the fine-bubble plume is almost identical to that of a particle falling in the quiescent water. Additionally, after the fine-bubbles have been separated from the particle surface, they flow into the wake of the particle, forming a stagnant region. The particle wake diameter increases threefold, as compared with its value in the downstream direction of the fine-bubble plume. [ABSTRACT FROM AUTHOR]