Particle image velocimetry in practice
Sammanfattning: Experimental fluid mechanics has for a long time been used to visualize flow phenomenon. An early pioneer was Ludwig Prandtl who used aluminum particles in water flumes to describe the flow in a qualitative manner. In line with the rapid development of Computational Fluid Dynamics, CFD, the need for new validation tools has increased. By combining Prandtls attempt to trace particles and contemporary tools in laser and computer technologies a quantitative non intruisiv whole field technique, so called Particle Image Velocity (PIV) has been developed. The PIV technique has been improved and grown in popularity through recent decades with the increase in computer capacity. This thesis describes three rather different areas of application of PIV measurements. In the first case PIV is used as pure measurement technology tool to describe the flow field inside an attraction channel in connection to fish migration. In the second case, PIV is applied as a validation tool for CFD calculations with Large Eddy Simulation(LES) including an extensive analysis of the results. 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. The attraction channel is a U-shaped channel designed to facilitate salmonoid like fihes to migrate upstream to their spawning grounds. The attraction channel has a restriction in the downstream outlet that provides an acceleration of the attraction water up to 38% of the sourunding water velocity according to the PIV measurements. With PIV measurements it is also shown that the depth of displacement over the restriction is significant for how far downstream the acceleration is perceptible. CFD technology is constantly evolving and new methods will become the future standard in the industry. In the current situation Reynolds Avereaged Numerical Simulations (RANS) is the most used method in CFD. But development is approaching LES technology. This is, for instance, motivated by energy production units which has many applications with high turbulence and temperature fluctuations. In the current situation it is required to extend the service life of existing power plants. Therefore it is desirable to be able to estimate these fluctuations impact on thermal loads on the materials inside the plant, for example 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. Double Restriction Sealings (DRS) have been used in bearings and other lubricated applications since the 1940's. A DRS is intended to prevent contamination from entering and is therefore used to increase the life span of lubricated parts, i.e. hinder polutants to reach the rolling elements in bearings for example. Although it is widly applied little is known about the actual function and mechanism of the DRS. To learn more about the flow and particle tracks within a DRS, a new method to visualize and quantify grease flow within a DRS has been developed based upon micro PIV. The main result from this study is that it is possible to make quantititative measurement of the flow within a DRS.
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