High-Resolution 2.5D Particle Image Velocimetry Measurements of the Flow Fields Generated by Small Fans

The free jets of an axial and a centrifugal fan have been scanned by a specialized particle image velocimetry (PIV) setup, which allows for volumetric scans of the time-averaged velocity field. Both of these fans have similar dimensions of approximately (70×70×25) mm3. A classic PIV setup 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 were captured by the first 2.5D scan. Another scan, with the fan rotated by 90 deg about its outlet surface normal, captured the missing third velocity component. This article describes the details of the measurement setup, and mentions measures concerning seeding, reflections, and calibration. In the signal processing stage, two independent sets of gathered image data had to be processed, producing two sets of velocity image frames. These were subsequently combined using gridded interpolation in order to obtain a three-dimensional velocity field. Specifically devised software tools allowed for a computational fluid dynamics(CFD)-like analysis and visualization of the flow field. Typical parameters of the generated jets, like the spreading and rotation rates, were calculated from the measurement data and details of the outlet flow fields were investigated. The interpolated data were also used to analyze the influence of an assumed coarser measurement grid resolution on the results for the obtained outletflow fields.