Flow visualisation is an experimental technique to view complex fluid flow in engineering components. Advanced modelling techniques and rapid prototyping are used to generate transparent models of components. The flows are modelled using a fluid having the same refractive index as the transparent model. To illustrate flow paths, the fluid is seeded using minute particles. A sheet of laser light is used to illuminate the model and allows the particles to be tracked through the component. Video footage and still images can be taken of the complex flow patterns and then, using a sophisticated image processing system, flow velocity measurements can be acquired. The technique has been successfully used to investigate flows in coolant passages, water and oil pumps, inlet manifolds and oil passageways.
Now available from VisEng: New Flow-Tek CCD portable flow visualisation equipment.
Modelling Techniques
Transparent Model of an Engine Block
A variety of modelling techniques which can be adapted to suit the individual requirement are available. However an innovative new technique has been developed for the production of complex flow models, which makes use of rapid prototyping models. This involves using the CAD data from the design to directly generate clear resin models of fluid passageways within components using the stereolithography process. This SLA model is then used in a casting process to generate a square sided model.
Imaging Techniques
Oil Pump
Animated Image of Flow Visualisation
A fluid matched for refractive index to the transparent model material and seeded with minute particles is then pumped through the model. The flows can then be illuminated with a sheet of laser light, giving an undistorted and very graphical real-time illustration of the fluid flows within the model. Detailed observation of the flow can show up areas of stagnation and turbulence. The technique can be applied to coolant, oil and air flows within engines and transmissions.
Particle Image Velociemetry (PIV) Technique
Particle Pairs / Vector Map of Velocities
PIV is a technique whereby velocities of fluids can be measured by photographing particles within the flows in two positions a short time distance apart. This is achieved by running the model as for flow visualisation but instead of using a continuous sheet of laser light, the laser is strobed twice over a known period of time. Storing the image as a PC graphics file, specialist software is used to identify the particle pairs and plot velocity vectors for each particle movement. This is then analysed and displayed as a coloured vector map. This coloured vector map can then be compared with computational studies which give an output in a similar format.
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PO Box 2623
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