New PIV-based techniques for turbulence research

Kurzfassung

Particle Image Velocimetry (PIV) has become a widely used technique for investigations into fluid flows were the spatial distribution of the velocity helps to understand the physics of flow. However, quiet often other quantities are desirable to answer fluid-mechanical questions. Time resolved PIV measurements in air flows as well as the simultaneous determination of all three velocity components in spatially separated planes for example are desriable for many fluid-mechanical investigations. In order to measure these quantities a multiple plane stereo PIV system has been developed. The multiple plane stereo PIV system consists of a four pulse laser system delivering orthogonally polarized light, two pairs of high resolution progressive scan CCD cameras in an angular imaging configuration with Scheimpflug correction for stereo-scopic recording, two high reflectivity mirrors and a pair of polarizing beam-splitter cubes. This technique is very reliable, robust and well suited for all kinds research, purely scientific as well as for industrially motivated investigations in large wind tunnel. Instantaneous quantities as the vorticity or the invariants of the velocity gradient tensor and time-dependent quantities as space-time correlations or the acceleration can be obtained to characterize the spatial and temporal flow unsteadiness. In order to study the accuracy and reliability of the Multiple Plane Stereo system the transition to turbulence in a flat plate boundary layer flow with zero pressure gradient has been examined