3D-Flow Measurement by Stereo Imaging

A new method to record three-dimensional liquid flow fields by using `Particle Tracking Velocimetry' is presented. It is based on a two-dimensional Particle Tracking Velocimetry method. It was extended to the third space dimension in order to include the complete physical space. This procedure allows to determine the Lagrange-flow field and to calculate from it the Euler-velocity flow field obtained from many other flow measuring techniques. A calibration method was developed for the wind-wave-flume which allows a high resolution in space. The stereo camera setup and the experimental setup were optimized for the liquid flow measurements. For the first time a liquid prism and a Scheimpflug-camera geometry was used. Numerical calculations using the finite element method demonstrate the complexity of the problem of dealing with free surfaces with wind-induced shear forces as a boundary condition. They show clearly that experimental studies are indispensable for describing phenomena such as `bursts' (descending of liquid elements from close to the surface into deeper layers). Flow measurements were performed in a newly constructed wind-wave-flume (AEOLOTRON) and in a smaller predecessor by using the newly developed imaging methods. In this way the flow fields of wind driven water waves could be characterized by the velocity field and the `turbulence' conditions.