<div class="section abstract"><div class="htmlview paragraph">The simulation of icing conditions in icing wind tunnels (IWTs) is a significant element in the certification of aircraft components and offers unique possibilities for research purposes. Up to 2014 only the conditions defined in Appendix C of the EASA Certification Specification 25, respectively the FAA Code of Federal Regulations Title 14 Part 25 were used for the certification processes in IWTs. In addition, Appendix O was introduced in 2014 to cover the supercooled large droplet (SLD) icing conditions of freezing drizzle and freezing rain, which pose a potential risk for flight safety. The simulation of SLD icing in IWTs is, due to the different behavior of the large droplets, very challenging and not all required conditions have successfully been recreated yet. RTA Rail Tec Arsenal Fahrzeugversuchsanlage GmbH has focused on the simulation of in-flight icing conditions since 2012 and increased effort was put in the simulation of SLDs in recent years. During several research projects funded by the Austrian government it was shown that droplet size distributions for freezing drizzle MVD > 40 μm and freezing rain MVD > 40 μm can be recreated close to the requirements. With further improvements to the spray system, a cloud uniformity within certain tolerances also has been achieved over areas large enough to cover an unscaled wing section. In order to determine the influence of the different droplet sizes on the aerodynamic performance, a NACA0012 wing section with a wingspan of 1.8 m and a chord of 1 m was exposed to different icing clouds including Appendix C conditions, freezing drizzle and freezing rain. The aerodynamic lift coefficient was recorded over a large angle of attack range and the characteristics of the different ice accretions were analyzed and documented using high resolution 3D scan technology. Furthermore, the drag increase during the icing process was measured. It was the first time that an unscaled wing was iced under artificial freezing rain conditions.</div></div>
Abstract. This work describes the latest design, calibration and application of a near-infrared laser diode-based photoacoustic (PA) hygrometer developed for total water content measurement in simulated atmospheric freezing precipitation and high ice water content conditions with relevance in fundamental icing research, aviation testing, and certification. The single-wavelength and single-pass PA absorption cell is calibrated for molar water vapor fractions with a two-pressure humidity generator integrated into the instrument. Laboratory calibration showed an estimated measurement accuracy better than 3.3 % in the water vapor mole fraction range of 510–12 360 ppm (5 % from 250–21 200 ppm) with a theoretical limit of detection (3σ) of 3.2 ppm. The hygrometer is examined in combination with a basic isokinetic evaporator probe (IKP) and sampling system designed for icing wind tunnel applications, for which a general description of total condensed water content (CWC) measurements and uncertainties are presented. Despite the current limitation of the IKP to a hydrometeor mass flux below 90 gm-2s-1, a CWC measurement accuracy better than 20 % is achieved by the instrument above a CWC of 0.14 g m−3 in cold air (−30 ∘C) with suitable background humidity measurement. Results of a comparison to the Cranfield University IKP instrument in freezing drizzle and rain show a CWC agreement of the two instruments within 20 %, which demonstrates the potential of PA hygrometers for water content measurement in atmospheric icing conditions.
Abstract. Supercooled large droplet (SLD) icing can occur behind the protected surfaces of an aircraft and create severe aerodynamic disturbances, which represent a safety hazard for aviation. Liquid water content (LWC) measurements in icing conditions that contain SLD require instruments that are able to sample unimodal and bimodal droplet size distributions with droplet diameters from 2 to 2000 µm. No standardized detection method exists for this task. A candidate instrument, that is currently used in icing wind tunnel (IWT) research, is the Nevzorov probe. In addition to the standard 8 mm total water content (TWC) collector cone, a novel instrument version also features a 12 mm diameter cone, which might be advantageous for collecting the large droplets characteristic of SLD conditions. In the scope of the two EU projects SENS4ICE and ICE GENESIS we performed measurement campaigns in SLD icing conditions in IWTs in Germany, Austria and the USA. We obtained a comprehensive data set of measurements from the Hotwire, the 8 mm and 12 mm cone sensors of the Nevzorov probe and the tunnel reference instrumentation. In combination with measurements of the particle size distribution we experimentally derive the collision efficiency curve of the new 12 mm cone for median volume diameters (MVDs) between 12 and 58 µm and wind tunnel speeds from 40 to 85 µm. Knowledge of this curve allows us to correct the LWC measurements of the 12 mm cone (LWC12) in particular for the inevitably high decrease in collision efficiency for small droplet diameters. In unimodal SLD conditions, with MVDs between 128 and 720 µm, LWC12 generally agrees within 20 % with the tunnel LWC reference values from a WCM-2000 and an Isokinetic Probe. An increase in the difference between LWC12 and the WCM-2000 measurements at larger MVDs indicates better droplet collision properties of the 12 mm cone. Similarly, the favorable detector dimensions of the 12 mm cone explain a 7 % enhanced detection efficiency compared to the 8 mm cone, however this difference falls within the instrumental uncertainties. Data collected in various bimodal SLD conditions with MVDs between 16 and 534 µm and LWCs between 0.22 and 0.72 g m-3 also show an agreement within 20 % between LWC12 and the tunnel LWC, which makes the Nevzorov sensor head with the 12 mm cone the preferred instrumentation for measurements of LWC in Appendix O icing conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.