Close-up analysis of inflight ice accretion

Reehorst, Andrew L.; Ratvasky, Thomas P.; Sims, J.R.

doi:10.2514/6.1994-804

Cited by 9 publications

(9 citation statements)

References 2 publications

(1 reference statement)

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“…The Reynolds numbers (based on the airfoil chord) tested were 0.75x10 6 , 1.25x10 6 and 2.25x10 6 . The extent of the distributed roughness was 0.125", 0.250" and 0.5" at locations of 4,7,8,12,18, and 24 mm from stagnation. His measurements showed that transition begins at, or very near the trailing edge of the roughness.…”

Section: Effect Of Large Roughness Elements On Boundary Layer Devementioning

confidence: 96%

“…They also observed that since feathers tended to spread out laterally, when the feather density is high, adjacent feathers will tend to merge. Reehorst et al 12 used the same experimental setup for close-up in-flight observations in the NASA Glenn Research Center's Twin Otter Icing Research Aircraft. They measured the effect of droplet size and water flux on the feather growth rate.…”

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confidence: 99%

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Current Experimental Basis for Modeling Ice Accretions on Swept Wings

Vargas

2007

Journal of Aircraft

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Section: Effect Of Large Roughness Elements On Boundary Layer Devementioning

confidence: 96%

mentioning

confidence: 99%

Current Experimental Basis for Modeling Ice Accretions on Swept Wings

Vargas

2007

Journal of Aircraft

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“…As the feathers grow, not only do they distort the oncoming and downstream flow, but they also constitute an added impingement region that protrudes into the flow. Therefore, droplets that bypass the stagnation area can be important due to their contribution to ice growth downstream [4]. This shows clear evidence for the necessity of accurate droplet trajectory calculations and for the importance of completeness of the water transport models.…”

mentioning

confidence: 89%

“…The MVD for these droplets can be on the order of 100 m. These droplets do not comply with the aforementioned assumptions and cause unpredictable ice shapes due to different underlying mechanisms. An example of the unpredictable features of the resultant ice shapes is the feather growth, which takes place beyond the calculated impingement region [4]. As the feathers grow, not only do they distort the oncoming and downstream flow, but they also constitute an added impingement region that protrudes into the flow.…”

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confidence: 99%

Investigation of Relative Humidity and Induced-Vortex Effects on Aircraft Icing

Ogretim¹,

Huebsch²,

Narramore³

et al. 2007

Journal of Aircraft

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Two new mechanisms for downstream ice growth (i.e., downstream of the primary ice shape) in aircraft icing scenarios were investigated. The first mechanism is local variation of relative humidity with its potential for water deposition due to supersaturation. The second mechanism is induced-vortex effects due to their potential impact on droplet paths. It was shown that for rough surfaces with an extended period of exposure, relative humidity effects can lead to additional growth. The resultant frost is a sandpaperlike roughness that can severely degrade the aerodynamic performance of the wings. It was also shown that the vortices induced by the existing ice-shape features are capable of altering the droplet paths. As a result, impingements occur beyond the limits predicted by the methods in other icing prediction codes.Nomenclature a x , a y = nondimensional acceleration component in the x and y directions a 0 , a 0 = acceleration component in the 0 and 0 directions a = reference value for the nondimensionalization of acceleration C p = pressure coefficient, P P 1 = 1 2 air V 2 1 c = chord length D = diffusivity of water vapor in air, m 2 =s e, e = actual and saturation vapor pressure, respectively, mbar h = height of the roughness element K = thermal conductivity of water, J=m s K L = latent heat of vaporization for water, 2:5 10 6 J=kg LER = leading-edge radius, m LWC, VWC = liquid and vapor water content, respectively, in kilograms of water per cubic meter of air MVD = median volumetric diameter, m N = number of droplets in 1 m 3 of air P = static pressure, Pa (unless otherwise stated) R v = specific gas constant for water vapor, 461 J=kg K RH w , RH ice = relative humidity with respect to liquid water and ice, respectively r = radius of the droplet, m S = cross-sectional area of a sphere, m 2 s d = separation between two neighboring droplets, m T = static temperature, K t = reference value for the nondimensionalization of time V 1 = velocity of the approaching flow v x , v y = nondimensional velocity component in the x and y directions v 0 , v 0 = velocity component in the 0 and 0 directions w = mixing ratio of water vapor and dry air = ratio of the specific heats air , v = density of dry air and water vapor, respectively, kg=m 3 water = density of liquid water, kg=m 3 = stream function

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“…-Droplet shape distortion leading to a different drag force, hence different path, than expected 33 , -Droplet break-up before impingement 33 , -Splashing, re-impingement and consequent water redistribution 34 , -Water film dynamics 12 , -Impact on heat transfer characteristics, and -Ice sublimation 35 .…”

Section: Chapter IV Mechanisms For Downstream Ice Growthmentioning

confidence: 99%

Investigation of relative humidity and induced-vortex effects on aircraft icing

Ogretim¹

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Aircraft icing is an area of research that has drawn attention since the early times of powered flight at high altitudes. Since World War II, aircraft icing research has gained a great deal of momentum, and several branches of research have developed as a result. These branches include the experimental, analytical and computational methods. With the advent of high-speed computers, the computational methods are becoming the leading icing research area due to their low cost requirements. However, a significant hindrance is the lack of a complete understanding of the icing phenomena, which leads to discrepancies between the predictions and the experiments. In recent years, there have been efforts to improve this situation by accounting for several mechanisms within the computational models. These mechanisms include the droplet splash and re-impingement, water film dynamics, and different heat transfer mechanisms. In support of enhancing the understanding of the aircraft icing process, this Ph.D. study focuses on the relative humidity effects and the interaction of the induced vortices with the droplets and the surface water. Currently the relative humidity effects are neglected in the icing prediction codes with the assumption that it can at best be a second-order effect. This Ph. D. study looks at the conditions in which the relative humidity effects can pose significant impact on the accreted ice shape. It was seen that the flow around the airfoil suction surfaces and the vortices, which have low-pressure cores, shed from the existing ice shape are highly supersaturated. Therefore, the suction surfaces and the aft regions of the main ice shape are exposed to condensation/deposition due to relative humidity effects. The time scales involved in the relative humidity effects were also investigated by using a numerical droplet growth experiment. In the particular case considered in this study, the required time to re-establish equilibrium, i.e. recover saturation conditions, varied from 12 milliseconds for droplets with 1 micron diameter to 5 seconds for droplets with 20 micron diameter. In an actual flight scenario, the direct impingement region mostly overlaps with the stagnation region, where the local flow is subsaturated. However, the water mass carried by the water droplets is much higher compared to changes that can be triggered by subsaturation. Therefore, it can be concluded that the collection efficiency in the direct impingement region will have negligible change despite the evaporation due to subsaturation. So, the relative humidity can at most be a secondary effect in the direct impingement region. However, exposure to supersaturated air for long periods can lead to localized frost growth beyond the direct impingement region. For a particular case considered in this study, it was found that there is a potential for the growth of extra ice roughness up to 0.4 mm over a 30 minute period. As far as the induced vortex phenomena, no past work has been done, because the ice accretion prediction codes are based ...

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Close-up analysis of inflight ice accretion

Cited by 9 publications

References 2 publications

Current Experimental Basis for Modeling Ice Accretions on Swept Wings

Current Experimental Basis for Modeling Ice Accretions on Swept Wings

Investigation of Relative Humidity and Induced-Vortex Effects on Aircraft Icing

Investigation of relative humidity and induced-vortex effects on aircraft icing

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