Abstract
The wake with positive buoyancy at the Reynolds number 300 and the Richardson number 0.3 of air was analyzed by the DNS computation, and revealed as follows : Positive buoyancy effects are that one is Effect I, that is, a decrease of the axial direction vorticity|ωz|, and the other is Effect II, that is, a decrease of the 3D motion, i. e. the vorticities |ωx|, |ωy| with the upward and horizontal directions, and the velocity |w| with the axial direction. Effect II is more dominant than Effect I.That is, the 3D motion moving right and left decreases remarkably, but the suppression of vortex street becomes weak. A space effect of Effect II is that the vortex dislocation becomes vague and a dislocation location becomes time-dependent. A time effect of Effect II is that the frequency of the 3D motion increases, the amplitude of the motion decreases, and the formation region length decreases. A space and time effect of Effect II is that the oscillation mode becomes the B mode with 1 of the wave length Λ, and 2fwake and 5fwake of the dominant frequency fp of the 3D motion in the nearwake, and the A* mode with 3 of Λ, 2fwake of fp, and the weak vortex-dislocation in the farwake, here fwake is the wake frequency.
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More From: TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B
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