FIEVel: a Fast InExpensive Velocimeter based on an optical mouse sensor*

Velocity measurement in fluids is essential for many applications spanning research, education, and industry. This presentation will discuss the development and application of FIEVel, a low cost, high sample rate, optical fluid velocimeter. State-of-the-art methods such as hot-wire anemometry, laser doppler velocimetry, acoustic doppler velocimetry, and particle image velocimetry (PIV) are typically intrusive, offer a low sample rate, or have a high cost. Using an optical sensor developed for commercially available computer mice, we demonstrate nonintrusive, time-resolved, 2-component, pointwise velocity measurements in the bulk of a flowing fluid at sample rates over 6 kHz, validated by direct comparison with high frame rate PIV. Our device uses inexpensive and interchangeable lenses intended for webcams and a custom 3D-printed housing with integrated focus adjustment. The device design, build documentation, supporting software, and operating guidelines are being released as an open-science hardware project and can be reproduced for less than $100 in materials. As an application example, we showcase the sensor's ability to resolve temporal spectra in grid generated turbulence.