PIV in Practice

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