Holographic Airborne for Cloud Particle Imager (HACPI): Development and Applications to Icing Wind Tunnels

Instruments for icing cloud particle characterization are prerequisites for icing wind tunnels in icing physics research and aviation certification. Yet, it is challenging to measure the multiple parameters of the multiscale and multiphase icing cloud particles, especially under an extremely hostile environment. To address this issue, a holographic airborne for cloud particle imager (HACPI) has been developed for icing cloud measurement. With the merit of 3-D imaging of holography, HACPI has the capability of simultaneously measuring particle morphology, size distribution, median volume diameter (MVD), and liquid water content (LWC), with a graphical user interface (GUI) software for remote control and real-time processing through parallel reconstruction. Aerodynamic simulations indicate relatively uniform flow characteristics within a sampling depth of 46 mm. The developed HACPI is applied to three industrial icing wind tunnels with test section scales ranging from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.6\times 0.6$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.0\times 2.0$ </tex-math></inline-formula>m. The elaborative designs of optical-mechanical–electronic-thermal integrations evidenced HACPI’s robust performance in high-speed wind up to ~200 m/s and low static temperature down to −30 °C. Results show that HACPI can accurately measure the icing clouds in the Code of Federal Regulations Title 14 Part 25 Appendix C, the bimodal supercooled large droplet (SLD) conditions in Appendix O, and the ice crystals in the Code of Federal Regulations Title 14 Part 33 Appendix D, with accuracies verified by side-by-side comparisons to certificated commercial instruments. HACPI has been demonstrated to be a powerful instrument for icing cloud measurement in icing wind tunnels and can be extended to other ground simulation facilities as well as aviation certification.