壁の面内振動による壁乱流の抵抗低減機構(<小特集>乱流せん断流の制御)

概要

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We investigate the mechanism of drag reduction of a turbulent flow in a channel by wall oscillation. DNS is carried out in which one wall of a two-dimensional channel is stationary but the other is in sinusoidal oscillation normal to the mean flow. The most effective oscillation period is adopted and about 35% reduction in drag is confirmed. For this case, generation terms of quasi-streamwise vorticity are examined from various points of view. It is shown that quasi-streamwise vortices which play a key role in sustaining wall turbulence are most strongly affected in the buffer layer. Vorticity production rate fluctuates with the phase of wall oscillation and is enhanced at some definite favorable phase but suppressed as a whole, in one pitch of oscillation. The stretching effect as well as tilting effect is important howevers, the latter affects mainly weak chaotic vortices and hence the role of the former which modulates coherent quasi-streamwise vortices is more substantial. The suppression of vorticity generation by stretching is due to the decrease of inclination angle of a vortex to a wall.
一般社団法人日本機械学会の論文
1997-01-25