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. The generation, transport and characterization of supercooleddroplets in multiphase wind tunnel test facilities is of great importancefor conducting icing experiments and to better understand cloudmicrophysical processes such as coalescence, ice nucleation, accretion andriming. To this end, a spray system has been developed, tested andcalibrated in the Braunschweig Icing Wind Tunnel. Liquid droplets in thesize range of 1 to 150 µm produced by pneumatic atomizers wereaccelerated to velocities between 10 and 40 m s−1 and supercooled totemperatures between 0 and −20 ∘C. Thereby, liquid water contents between 0.07 and 2.5 g m−3 were obtained in the testsection. The wind tunnel conditions were stable and reproducible within3 % standard variation for median volumetric diameter (MVD) and 7 %standard deviation for liquid water content (LWC). Different instrumentswere integrated in the icing wind tunnel measuring the particle sizedistribution (PSD), MVD and LWC. Phase Doppler interferometry (PDI), laserspectroscopy with a fast cloud droplet probe (FCDP) and shadowgraphy weresystematically compared for present wind tunnel conditions. MVDs measuredwith the three instruments agreed within 15 % in the range between 8 and 35 µm and showed high coefficients of determination(R2) of 0.985 for FCDP and 0.799 for shadowgraphy with respect to PDI data. Between 35 and 56 µm MVD, the shadowgraphy dataexhibit a low bias with respect to PDI. The instruments' trends and biasesfor selected droplet conditions are discussed. LWCs determined from massflow calculations in the range of 0.07–1.5 g m−3 are compared to measurements of the bulk phase rotating cylinder technique (RCT) and the above-mentioned single-particle instruments. For RCT, agreement with the mass flow calculations of approximately 20 % in LWC was achieved. For PDI 84 % of measurement points with LWC&lt;0.5 g m−3 agree with mass flow calculations within a range of ±0.1 g m−3. Using the different techniques, a comprehensive wind tunnel calibration for supercooled droplets was achieved, which is a prerequisite for providing well-characterized liquid cloud conditions for icing tests for aerospace, wind turbines and power networks.

Comparison of different droplet measurement techniques in the Braunschweig Icing Wind Tunnel