Within the European ICE GENESIS project, the deliverable D4.1 is closely related to Task 4.1 of work package 4 (“Instrumentation for liquid icing conditions”). This task is dedicated to the review and the selection of the most appropriate instrumentation for measurement of the particle size distribution (PSD) under Appendix O conditions in various wind tunnel (W/T) facilities. The SLD measurements requirements are extracted from FAR/CS-25 Appendix C & O (FAA, 2014). In particular, this task deals with:
a) Selection of the best instrumentation required to measure PSD under appendix O conditions with focus on supercooled large droplets (SLD), using optical array and scattering probes. The respective W/T installation requirements should be considered.
b) Calibration of selected instruments regarding sample area and particle size with SLD droplet generators in the laboratory.
c) Evaluation of PSD under Appendix O conditions with respect to appropriate correction methods for image processing and uncertainty assessment.
An overview and aspired performance targets for App O conditions in wind tunnel facilities were given in D3.1 “Definition of the target requirements for test facilities operating envelopes for App O”. In this deliverable D4.1, state of the art instrumentation to characterize number concentrations and particle sizes for SLD conditions are reviewed. The main focus of this report is on supercooled large droplets with a defined maximum diameter range of 100 to 500 μm for freezing drizzle environments. But also instruments to measure droplet diameters larger than 500 μm for freezing rain conditions and for a smaller particle size range are included in the discussion. The latter represent measurement techniques with a measurement size range from 1 μm up to 150 μm, useful to characterize Appendix C conditions and the lower side of PSD (e.g. the first part of the bi-modal distribution) for Appendix O conditions.
The chosen instrumentation will be provided by the participating test facilities (CIRA, RTA, CIAM, TsAGI, MINDEF) or by independent research institutes (DLR, CNRS) that can be used as reference in several test facilities. The work of task 4.1 indicates the best instrumentation that can be used in W/T calibration and is therefore essential for work package 6 “SLD test capability”. The calibration of selected instruments as well as the evaluation of correction methods and uncertainty assessment during data analysis will help to reduce the risk of facility calibration bias for aircraft icing certification programs in Appendix C and O.
The particle sizing instruments can be divided by their measurement techniques into two main groups: scattering probes and optical array probes. The advantages and data analysis methods for both techniques will be discussed in the context of their nominal particle size ranges. Since, both W/T facilities and independent research institutes are collaborating in this task, all partners can benefit from each other. To ensure the best possible results on the calibration of SLD conditions in W/T facilities, the facilities have to consider installation possibilities and constraints of homogeneous LWC in the test sections.
The main objectives we have to meet with the selected PSD instrumentation for icing wind tunnels are summarized below. These objectives consider ongoing discussions related to W/T SLD test capabilities (WP6), W/T tests for liquid and snow conditions (WP8) and numerical capabilities (WP9).
a) Guarantee a wide measurement range for particle sizes between 1 μm and several millimetres to cover Appendix C and Appendix O (freezing drizzle and freezing rain) conditions by using state of the art scattering probes or optical array probes.
b) Provide correction methods to correct the sizing of the out-of-focus images (Korolev, 2007) and the fragmented droplet images that may be undersized, while resulting in an overestimated concentration of small droplets.
c) Give a reasonable uncertainty assessment for the employed measurement techniques.
Since, the calibration of SLD conditions in the W/T test facilities in WP6 will focus on FZDZ conditions, the discussion of the instrumentation selection is in this context, too. A summary and detailed information of the chosen PSD instrumentation of each participated W/T test facility will be shown in a table in the “Appendix: PSD instrumentation selected for wind tunnel tests in SLD conditions (FZDZ) within ICE GENESIS”.
