密度成層流における振動円柱からの渦放出

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Vortex shedding from a sinusoidally oscillating horizontal circular cylinder in a stratified fluid with constant density gradient is studied by numerical experiment based on finite-volume solution of the Navier-Stokes equation for a heterogeneous fluid, the continuity equation and the transport equation for solute. To validate the computational method to the flow field with small density fluctuation we perform the computation at Kc=1 at which the amplitude of the oscillation is relatively small and compare the result with the linear theory of the internal gravity wave with small amplitude. The computed results show that the internal waves are generated with the conditions and the direction of propagation identical with those predicted by the theory. We also perform the experiment at Kc=5 in the range of Fn=2.0 ∼ 0.2 to examine the effects of density stratification on vortex shedding which would occur in a homogeneous fluid at this Kc number. For the range of Fn >__- 0.6 the stratification weakens the rotational motion as well as the diffusion of vorticity so that it prevents the process of the generation, movement and shedding of vortex and as a result both in-line and lift forces decrease with the Froude number decreasing. For The range of Fn <__- 0.4 vortex shedding does not occur but vorticity is generated away from the cylinder as well, and such a relatively wide distribution of strong vorticity leads to the increase of drag force.
社団法人日本船舶海洋工学会の論文
1996-03-25

密度成層流における振動円柱からの渦放出

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