PIV in Practice

Abstract: Experimental fluid mechanics has for a long time been used to visualize flow phenomenon qualitatively. Traditionally, visualization has been done with dye or tracer particle due to their ability to follow the flow pattern well. One of the early pioneers in experimental fluid mechanics was Ludwig Prandtl who used mica particles in water flumes to accurately describe the flow around wing profiles. Due to Prandtl’s results in the early 20th century, some of the most important theories in aviation were founded. By combining Prandtl’s attempt to trace particles, and contemporary laser and computer technologies a quantitative non-intrusive whole field technique, so called Particle Image Velocimetry (PIV), has been developed. The PIV technique has through the advances in computer science the recent decades, been improved significantly and has also grown in popularity among the scientific- and technological community. This thesis describes implementation of PIV in several diverse research areas from macro- to micro scale. First, it is described how PIV is used as a pure measurement technique to understand complex flow phenomena. The technique is demonstrated on a small U-shaped channel designed to facilitate salmonoid like fishes upstream migration to their spawning grounds. Second, PIV is used as a validation tool for Computational Fluid Dynamics, CFD. In the current situation, CFD is undergoing a generation shift from Reynolds Averaged Numerical Simulation, RANS, to Large Eddy Simulations, LES. This is for instance motivated by energy production units which has many applications with high turbulence and temperature fluctuations. Hence it is desirable to be able to estimate the impact on thermal loads on the materials inside the plant (e.g. the pipe walls). An LES approach is superior to applying to RANS since the large eddies are resolved. However, LES is still not mature enough to be used without validation in critical applications. Therefore, PIV has been used to create a validation database for a generic T-junction. Finally, a description of how PIV technique can be adopted to study the flow of complex fluids in small geometries by means of microscopy, is given and applied on lubrication grease flow in labyrinth seals which have been used in bearings and other lubricated applications since the 1940’s. The intention with labyrinth seals is to lubricate the bearing and prevent contamination from entering the rolling elements. Although it is widely applied, little is known about the actual function and mechanism of labyrinth seals. To learn more about the flow and particle migration within a seal geometry, a new method to visualize and quantify grease flow within a labyrinth seal has been developed based upon micro-PIV.