High resolution 2.5D PIV measurements of the flow fields generated by small fans
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The free jets of an axial and a centrifugal fan have been scanned by a specialized particle image velocimetry (PIV) set-up, which allows for volumetric scans of the timeaveraged velocity field. Both of these fans have similar dimensions of approximately 70mm × 70mm × 25mm. A classic PIV set-up was combined with a precise linear stage to move the fans through the laser fan beam in small steps, creating a dense array of measurement planes. Two components of the time-averaged velocity field are captured by the first 2.5D scan. Another scan, with the fan rotated by 90° about its outlet surface normal, captures the missing third velocity component. This article describes the details of the measurement set-up, and mentions measures concerning seeding, reflections, and calibration. In the signal processing stage, two independent sets of gathered image data have to be processed, producing two sets of velocity image frames. These are subsequently combined using gridded interpolation in order to obtain
a 3D velocity field. Newly devised software tools enable us to view any slice through the data. This way, movies can be made, which visualize changes of the flow field while moving through it. Details of the flow are discernible, and typical parameters of the generated jets, like the spreading rate, are calculated from the measurement data.