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HYDRODYNAMICS AND ACOUSTICS

2018 ◊ Volume 1 (91) ◊ Issue 3 ◊ p. 284-301

V. A. Voskoboinick*, A. A. Voskoboinick*, A. V. Voskoboinick*, V. M. Stepanovich*, I. A. Hyzha*

* Institute of Hydromechanics of NAS of Ukraine, Kyiv, Ukraine

Vortex motion inside the hole of a complex geometry

Gidrodin. akust. 2018, 1(3):284-301

https://doi.org/10.15407/jha2018.03.284

TEXT LANGUAGE: Ukrainian

ABSTRACT

The paper presents the results of visual study of generation and evolution of the vortex flow inside the holes in the form of single V- and Λ-shaped grooves on a flat surface streamlined with a flow at different angles. The mentioned holes were obtained as a result of mating two oval fragments with an elongation of 2. The primary flow velocities varied within U=(0.1 ... 0.5) m/s that corresponds to the interval Red=Ud/ν=(4...20) x103 for the Reynolds numbers calculated by the diameter of the groove. The visualization was performed using the specially developed water-soluble coatings and contrasting colors with zero buoyancy that were injected to the wall flow layer. The generation of the vortex structures was not observed in the presence of a laminar flow inside the cavities of complex geometry. For a transitional or turbulent flow inside the V-shaped hole, the horseshoe vortex structures were formed that decreased in size and pressed against the separation wall of the groove with the increase of velocity. Simultaneously, the periodic ejections of the small-scale vortex sheet were observed in mid cross-section of the groove. The spiral vortex structures generated inside the Λ-shaped hole were periodically ejected and propagated in the wake of the hole forming the pairs of counter-rotating vortices. Changes in the process of formation and ejection of vortex structures were noticed when varying the inclination angle of the V- and Λ-shaped holes in the plate's plane. For the laminar flow, the Strouhal number of the potential fluid ejection was ranged within 0.05 to 0.14. In the conditions of transition and turbulent flows, the Strouhal number of ejection of the vortex structures and vortex sheets increased from 0.15 to 0.5.

KEY WORDS

cavity, visualization, coherent vortex structure, vortex sheet, ejection, the Reynolds number, the Strouhal number

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