The Deliverable D4.2 of the European ICE GENESIS project deals with the “review, assessment and selection of instrumentation for LWC”. It is closely related to Task 4.2 of the work package 4. This task is dedicated to the review and selection of the most appropriate instrumentation for measurements of the liquid water content (LWC) under Appendix C and O conditions in wind tunnel (W/T) facilities. In particular, task 4.2 deals with the:
a) Selection of the best instrumentation required to measure LWC under Appendix C/O conditions in W/T facilities. The W/T installation requirements have to be taken into account.
b) Evaluation of the LWC measurements with respect to appropriate correction methods and uncertainty assessment.
Within this document, state-of-the-art instrumentation to characterize the LWC of small droplets and supercooled large droplets (SLD) is reviewed. The measurement requirements are extracted from FAR/CS-25 Appendix C & O conditions (FAA, 2014). The instruments should cover the LWC range from 0.01 g m-3 to 3 g m-3 for Appendix C. For Appendix O and SLD conditions, the icing envelope for LWC includes LWC lower than 0.5 g m-3 for all FZDZ and FZRA cases. Further the instruments should be able to detect small droplets with sizes larger than 1 μm as well as SLD with a maximum diameter range of 100 to 500 μm for freezing drizzle (FZDZ) environments and droplet diameters larger than 500 μm for freezing rain (FZRA) conditions.
The recommended instrumentation is either provided by the participating test facilities (CIRA, MinDef and RTA) or by independent institutes (CU, DLR) as reference in several test facilities. The work of task 4.2 is to select best available instrumentation for the calibration of SLD conditions in W/T facilities and is therefore essential for work package 6. The calibration of selected instruments as well as the evaluation of correction methods and uncertainty assessment during data analysis provides a reference setup for W/T facilities and helps to reduce the risk of facility calibration bias for aircraft icing certification programs in Appendix C and O.
Liquid water content instruments are bulk measurement devices and often used in wind tunnel as well as aircraft experiments. The LWC is derived as an integral over the whole droplet size spectrum. Direct information on the droplet size or the distribution of the LWC on different sizes is not possible. Therefore, it has to be known if an instrument can measure all droplet sizes with the same efficiency. Otherwise, correction methods have to be implemented with respect to simultaneously measured particle size distribution (PSD) or information about the median volume diameter (MVD) of a distribution. The document will discuss data analysis methods of each selected instrument in the context of Appendix C/O conditions.
The instrumentation will be used for the calibration of SLD conditions in W/T facilities (WP6), which means the facilities have to consider installation possibilities and constraints of homogeneous sampling test sections.
The main objectives to meet with the selected LWC instrumentation for icing wind tunnels are summarized below. The objectives consider discussions related to W/T SLD test capabilities (WP6), W/T tests for liquid and snow conditions (WP8) and numerical capabilities (WP9).
Objectives:
a) Guarantee a wide measurement range for the LWC (nearly three orders of magnitudes starting from 0.01 g m-3). Expected droplet sizes range between 1 μm and several millimetres to cover Appendix C and SLD conditions under Appendix O.
b) Provide correction methods for bulk measurements with respect to varying collection efficiencies of different droplet size spectra.
c) Give a reasonable uncertainty assessment for the used measurement techniques.
While instrument uncertainties are given for the complete set of instruments, three instruments were selected and have proven good performance for icing W/T measurements in Appendix C conditions. Results show that the Isokinetic Probe IKP, the WCM-2000 and the Nevzorov probe agree within better than 10% for LWC measurements in Appendix C conditions for LWC between 0.4 and 2.4 g/m³.
Tests with bimodal particle size distributions in Appendix O FZDZ conditions with MVD > 40μm at RTA at LWC between 0.4 and 0.6 g/m³ generally show a sufficient agreement with < 25% deviation of the results of the individual instruments from the multi instrument mean. The WCM2000 was closest to the multi instrument mean with deviations <1%. Compared to the multi instrument mean up to 10% deviation was detected for the Nevzorov 8 mm cone. The IKP trend tends to overestimate by ~20% the measurement conditions between 0.4 and 0.6 g/m³ of LWC. However, in addition to challenges in subtracting high levels of water vapour for background correction from a small LWC content, inhomogeneities in IWT particle distributions of up to 20% may significantly contribute to this bias. Additional measurements are required to derive respective uncertainties and to better constrain the homogeneity and humidity measurements at low LWC conditions.
The document has been adapted for export control. Therefore, DLR contribution of technical data has been removed due to export control unsolved issues.
