Experimental study of vorticity filaments in a turbulent swirling flow

We study vorticity fluctuations in a turbulent von Karman swirling flow generated in the gap between coaxial contra-rotating disks. The how is probed acoustically by an ultrasonic incident wave and the scattered pressure reveals intense vorticity concentrations which occur intermittently in the bulk of the flow. They are compatible with low pressure tube-like structures visualized in the same flow [Douady et al., Phys. Rev. Lett. 67 (1991) 983-986] and quantified with pressure measurements [Fauve et ai., J. Phys. II (France) 3 (1993) 271-278]. Their core size scales like the Taylor microscale as the Reynolds number is varied. Their statistical properties are analyzed in details and are found to be similar to those of pressure fluctuations. Copyright (C) 1998 Elsevier Science B.V.