Icing Wind Tunnel Measurements of Supercooled Large Droplets Using the 12 mm Total Water Content Cone of the Nevzorov Probe

Abstract

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.

MOSAiC-ACA and AFLUX - Arctic airborne campaigns characterizing the exit area of MOSAiC

“…Nevzorov. During the flight campaigns, a Nevzorov probe 101,102 (designed by Sky Physics Technology, Woodbridge, ON, Canada) was installed on the fuselage of Polar 5 aircraft. The Nevzorov probe is a constant-temperature, hot-wire probe designed for the airborne bulk measurements of the LWC and total water content (TWC) of clouds in 1 Hz resolution.…”

Overview of Cloud Microphysical Measurements during the SENS4ICE Airborne Test Campaigns: Contrasting Icing Frequencies from Climatological Data to First Results from Airborne Observations

“…For the Phenom 300, two instruments were chosen as the reference instrumentation for the campaign: a cloud combination probe (CCP) owned and operated by Embraer and an ice crystal detector (ICD) [15] operated by SEA. The CCP was previously used in SENS4ICE during the wind tunnel measurement and therefore the instrument's data evaluation is done as described in [6]. The combination of droplet spectra between 2 and 960 μm and liquid water content measurement provided a good base to differentiate between small and large droplet icing.…”

“…The optical sensors are deployed together with bulk liquid and total water content (TWC) instruments such as the Nevzorov Probe (ATR-42) [6,16] and the Ice Crystal Detector (ICD) (Phenom 300) [15], also well known for the use of droplets and glaciated cloud conditions. Next to classical scattering spectrometers (CDP) and optical array probes (CIP (Cloud Imaging Probe) and PIP (Precipitation Imaging Probe) from Droplet Measurement Technologies (DMT) ) [17], Artium's High Speed Imager (HSI) [18] using a 2D-CMOS array for particle images, and a multi-beam illumination will provide additional high resolution information for particles below 100 μm, where uncertainties remain due to the depth of field criterium.…”

“…Image analysis is performed with a Python-based code developed at DLR and described in [6,19]. Particles were filtered by shape (phase) to select the type of icing conditions (mixed phase and supercooled droplet icing).…”

“…1). The instruments used during the flight campaigns of SENS4ICE were previously used in wind tunnel tests of SLD and Appendix C conditions [6] and on other aircraft in icing conditions [7] to test and improve their working principle. For consistency and to reduce the uncertainty related to different measurement principles, the same instruments were chosen in order to compare different droplet spectra among the tunnels and to provide valuable information on the collision efficiency of bulk water content instruments.…”