PIV, LIF and 3D-PIV measurements applied on the wake behind a sphere
by
J. Nunez v. Voigt
Hermann Föttinger Institut
Coauthors: Prof.H.E. Fiedler, Dipl-Ing. A. Ziemann

To analyse the dynamic of coherent structures and the vortex structures themselves, three dimensional measurements are required. In comparison to the wake of a cylinder, the wake of a sphere is more difficult to investigate due to the complex flow-structures and the strong three-dimensional character of the flow. With PIV ( Particle Image Velocimetry ) we can apply a non introducive method to measure an instantanious two dimensional velocity field but to investigate the behavior and to get information about possible active influence on the flow this is not enough.

So the idea of a three dimensional measurement was performed with LIF (Laser Induced Fluorescence ) and a 3-D-PIV system was tested in the wake of a sphere at Reynolds-numbers (Re=U*D/nu) in the range of 100 to 700. The measurement techniques provides interesting and good qualitative and quantitative results on the wake of the sphere at stationary and starting flows, like the dynamic of vortex loop structures, and the description about the vortex loop length.

Date received: January 28, 1999