Shear instability inhibition in a cylinder wake by local injection of a viscoelastic fluid

The wake behind a circular cylinder in water is visualized when colored solutions are injected through rows of holes pierced in the cylinder. When these solutions are viscoelastic, a drastic change of the shape of the wake is observed compared to that observed for water injections. The aspect ratio of the wake is decreased, the wavelength of the vortices is increased, and a large region of slow fluid motion is developed behind the cylinder. It is shown that these observations are consistent to a sheer instability inhibition due to a local elasticity. (C) 1999 American Institute of Physics. [S1070-6631(99)02302-8].