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Three-dimensional turbulent offset jets were investigated using a particle image velocimetry technique. Detailed measurements were performed for offset height ratios of 0, 2 and 4. The presence of backflow influenced the distribution of the mean velocity and Reynolds stresses. A two-point correlation analysis was used to investigate the spatial distribution of large-scale structures within the inner shear layer of the flow domain. The results revealed that large-scale structures dominate the inner layer of the self-similarity region. Proper orthogonal decomposition was performed on the fluctuating velocity field within the symmetry and lateral planes using the snapshot approach. Results from the reconstructed field provided insight into the contributions of the most energetic structures to the turbulence statistics. The energetic structures contributed more to the Reynolds shear stress and streamwise turbulence intensity, while contributing less to the wall-normal turbulence intensity.

A three-dimensional offset jet flow over a surface mounted square rib was investigated using particle image velocimetry at Reynolds number of 7600. The square rib was mounted at three different locations downstream of the nozzle exit. Contour and profile plots in the symmetry plane were used to investigate the effect of the rib on the mean flow distribution and turbulence statistics. Changing the rib location enhanced the mixing and entrainment characteristics of the jet thereby leading to larger wall-normal spread rates. The quadrant analysis revealed a significant contribution of all events towards the Reynolds shear stress. The joint probability density function analysis showed that the structures within the outer shear layer of the jet differed from those of boundary layers. Results from the two-point correlation analysis indicated that the introduction of a surface mounted rib modified the flow structures within the developing region. However, there was no significant structural difference between the flow with mounted rib and the no rib case within the self-similar region. The proper orthogonal decomposition was used to examine how changes in rib location modified the dynamics of the energetic modes towards the turbulent kinetic energy and Reynolds shear stress within the developing and self-similar regions.

Experimental flow visualization is a valuable tool for analyzing microfluidics and nanofluidics in a wide variety of applications. Since the late 1990s, considerable advances in optical methods and image postprocessing techniques have improved direct optical measurements, resulting in an accurate qualitative and quantitative understanding of transport phenomena in lab-on-a-chip capillaries. In this study, a comparison of different optical measurement techniques is presented. The state-of-the-art development of particle image velocimetry to date, particularly in microscale applications, is reviewed here in detail. This study reviews novel approaches for estimating velocity field measurements with high precision within interrogation windows. Different regularization terms are discussed to demonstrate their capability for particle displacement optimization. The discussion shows how single- and multi-camera optical techniques provide two-dimensional and three-component velocity fields. The performance of each method is compared by highlighting its advantages and limitations. Finally, the feasibility of micro resolution particle image velocimetry in bioapplications is overviewed.

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