DHMPIV and Tomo-PIV measurements of three-dimensional structures in a turbulent boundary layer

In turbulent boundary layers, a large portion of total turbulence production happens in the near wall region, y/δ < 0.2. The aim of the present work is to measure three-dimensional velocity field in a turbulent boundary layer at a moderately high Reynolds number. Tomographic particle image velocitmery (Tomo-PIV) was used to extract the 3C-3D velocity field using a rapid and less memory intensive reconstruction algorithm. It is based on a multiplicative line-of-sight (MLOS) estimation that determines possible particle locations in the volume, followed by simultaneous iterative correction. Application of MLOS-SART and MART to a turbulent boundary layer at Reθ=2200 using a 4 camera Tomo-PIV system with a volume of 1000×1000×160 voxels is discussed. In addition, near wall velocity measurement attempt made by digital holographic microscopic particle image velocimetry (DHMPIV). The technique provides a solution to overcome the poor axial accuracy and the low spatial resolution which are common problems in digital holography [5]. By reducing the depth of focus by at least one order of magnitude as well as increasing the lateral spatial resolution, DHMPIV provides the opportunity to resolve the small-scale structures existing in near wall layers.