Evaluation of the Water Film Weber Number in Glaze Icing Scaling

Icing scaling tests were performed in the NASA Glenn Icing Research Tunnel to evaluate a new scaling method, developed and proposed by Feo for glaze icing, in which the scale liquid water content and velocity were found by matching reference and scale values of the nondimensional water-film thickness expression and the film Weber number. For comparison purpose, tests were also conducted using the constant We(sub L) method for velocity scaling. The reference tests used a full-span, fiberglass, 91.4-cm-chord NACA 0012 model with velocities of 76 and 100 knot and MVD sizes of 150 and 195 microns. Scale-to-reference model size ratio was 1:2.6. All tests were made at 0deg AOA. Results will be presented for stagnation point freezing fractions of 0.3 and 0.5

Efficient Coding of Local 2D Shape

Efficient coding provides a concise account of key early visual properties, but can it explain higher-level visual function such as shape perception? If curvature is a key primitive of local shape representation, efficient shape coding predicts that sensitivity of visual neurons should be determined by naturally-occurring curvature statistics, which follow a scale-invariant power-law distribution. To assess visual sensitivity to these power-law statistics, we developed a novel family of synthetic maximum-entropy shape stimuli that progressively match the local curvature statistics of natural shapes, but lack global structure. We find that humans can reliably identify natural shapes based on 4th and higher-order moments of the curvature distribution, demonstrating fine sensitivity to these naturally-occurring statistics. What is the physiological basis for this sensitivity? Many V4 neurons are selective for curvature and analysis of population response suggests that neural population sensitivity is optimized to maximize information rate for natural shapes. Further, we find that average neural response in the foveal confluence of early visual cortex increases as object curvature converges to the naturally-occurring distribution, reflecting an increased upper bound on information rate. Reducing the variance of the curvature distribution of synthetic shapes to match the variance of the naturally-occurring distribution impairs the linear decoding of individual shapes, presumably due to the reduction in stimulus entropy. However, matching higher-order moments improves decoding performance, despite further reducing stimulus entropy. Collectively, these results suggest that efficient coding can account for many aspects of curvature perception

Pr\ue9cipitation gla\ue7ante sur les surfaces portantes

As a part of its investigation, the Commission of Inquiry into the Air Ontario Crash at Dryden, Ontario asked the National Research Council to estimate the quantity and form of the precipitation adhering to the Fokker F-28's wings during its ill-fated take-off attempt.La Commission d'enqu\ueate sur l'\ue9crasement d'un avion d'Air Ontario \ue0 Dryden (Ontario) a demand\ue9 au Conseil national de recherches Canada d'estimer la quantit\ue9 et la forme de pr\ue9cipitation qui a adh\ue9r\ue9e aux ailes du Fokker F-28 au moment de sa malheureuse tentative de d\ue9collage.NRC publication: Ye

Ice Shape Sensitivity to Condition Variation

NRC publication: Ye

Calibration of NRC's Engine Test Cell Icing Nozzle Droplet Size Distribution

NRC publication: Ye

Winter Precipitation and its impact on wing aerodynamics

NRC publication: Ye

A Comparison of Droplet Sizing Instruments at NRC's Altitude Icing Wind Tunnel (AIWT)

NRC publication: Ye

Experimental assessment of a water-film-thickness weber number for scaling of glaze icing

AIAA 2001-0836: The evidence indicates that current practices for scaling of glaze icing tests do not recognize one or more important parameters. A Weber number based on a measure of the thickness of the liquid water film formed on the surface of the accreting ice has been proposed in another paper as the required additional scaling parameter. The present paper reports on experiments specifically designed to assess this proposal. Icing wind tunnel tests were done on 45 mm and 20 mm circular cylinders; the former constituted the reference cases and the latter, the sub-scale cases. In all sub-scale tests the accumulation parameter, the droplet inertia parameter and the calculated freezing fraction were made equal to the corresponding reference values. Freestream velocity for sub-scale test runs was chosen using several scaling parameters, including the newly proposed one. It was found that reasonably good similarity of ice accretion shapes was obtained for all of the sub-scale velocities that were tried, provided that the freestream static temperature was the same as that in the reference case. Possible explanations are suggested. When sub-scale freestream static temperature was the same as the reference value, the freestream velocities determined using Weber numbers based on water-film thickness and on droplet size were approximately equal, and this velocity gave marginally better similarity of ice shapes than velocities chosen on other bases. Solid aluminum and solid Plexiglas models gave essentially the same ice shapes for corresponding conditions. Most of the findings of the work are very preliminary and much more work is required to explore them.Peer reviewed: YesNRC publication: Ye

Recent developments in scaling methods for icing wind tunnel testing at reduced scale

This paper is concerned with reduced scale testing of in-flight ice accretion on aircraft surfaces. A basic description of the icing process is presented and the reason for occurrence of two types of icing, rime and glaze, is explained. Important physical phenomena are highlighted, including phenomena whose importance is not widely recognized. The implied modelling requirements are outlined and discussed. It is shown that the requirements can be readily satisfied for rime icing conditions and that good reduced scale test results can be obtained. For glaze icing on the other hand, not all of the scaling requirements are known. Recent developments in this area are outlined and discussed in the light of experimental results obtained by the authors and others.Peer reviewed: YesNRC publication: Ye

Wind Tunnel Wing Section Performance with De/Anti-icing Fluids and Freezing Precipitation

NRC publication: Ye