This paper describes experiments performed in an altitude chamber at the National ResearchCouncil of Canada (NRC) as the first step towards developing altitude scaling laws and procedures that will possibly allow aero-engines to be certified for operation in ice crystal clouds at high altitude by testing in sea level facilities. The principal objective was to test the hypothesis that accretion within a compressor due to ice crystal ingestion occurs when the local ratio of freestream liquid water content (LWC) to total water content (TWC) lies within a critical range at an accretionsusceptible location. If this hypothesis is correct, the local LWC/TWC ratio is the key parameter that must be matched in tests at low and high pressures to match accretions. Experiments were conducted in a small wind tunnel with an axisymmetric test article, consisting of a hemispherical nose attached to a conical afterbody, at a fixed TWC over a range of LWC/TWC ratios at (absolute) pressures of 34.5 kPa and 69 kPa to test the hypothesis. The LWC/TWC ratio was varied by changing the wet bulb temperature. Accretion steady-state volumes and growth rates measured at the two pressures were compared at conditions which were analytically predicted to produce matched LWC/TWC ratios. Good agreement was achieved in all cases. Accretion growth was greatest for LWC/TWC ratios in the range 10-25%. Additional tests demonstrated that wet bulb temperature, which was identified as an important variable in earlier studies, had little influence on accretion growth beyond its effect on LWC/TWC (i.e. ice particle melting). Tests were also conducted to determine whether accretion growth scales linearly with TWC at constant LWC/TWC. Those tests confirmed that not only does the accretion growth rate in the early growth phase scale in direct proportion to TWC , but so does the final size of the accretion. A simple semi-empirical model for predicting this behavior is described. While most of the tests were conducted with an ice particle median volumetric diameter of 45μ, some of the scaling tests were repeated with larger particles, which produced smaller accretions. Nomenclature& a, b = TWC-dependent coefficients in relation for t A = surface area C p = specific heat of air at constant pressure C ice = specific heat of ice d = diameter h c = heat transfer coefficient L evap = latent heat of vaporization of water L f = latent heat of fusion of water L subl = latent heat of sublimation of ice IWC = Ice Water Content (g/m 3 ) LWC = Liquid Water Content (g/m 3 ) m = mass = mass flow rate 1 = mass flux (mass flow rate per unit area) M = Mach number MVD = median volume diameter of ice particles, micrometer NRC = National Research Council of Canada Nu = Nusselt number (= h c d/k) p = pressure p ref = reference pressure (10 5 Pa) Pa = Pascal (N/m 2 ) Pr = Prandtl number (= µC p /k) = heat flux r = radius RATFac = Research Altitude Test Facility Re = Reynolds number (= ρUd/µ) t = accretion thickness t o = accretion thickness at stagnation point t & = thickness growth...

This paper describes the commissioning of a new test apparatus intended to simulate an inner-compressor duct bleed slot. It also identifies, for the first time, that ice crystal particle size plays an important role in the ice crystal phenomenon. Data and sample images of accretion are presented for wet bulb temperatures near freezing. The effect of wet bulb temperature and particle size on the natural melting of ice crystals is investigated. In addition, the erosion of surface accretion by ice crystal particles is discussed. NomenclatureFAA = Federal Aviation Administration GTL = Gas Turbine Laboratory IWCi = Ice Water Content injected (g/m 3 ), based on ice flow rate and test section volume airflow kPa = kilopascal LWC i = Liquid Water Content injected (g/m 3 ) with supplemental spray nozzles, based on water flow rate and test section volume airflow LWC m = Liquid Water Content (g/m 3 ) measured with SEA WCM-2000 multi-wire instrument Mach = Mach number MMD = median mass diameter of ice crystals MVD = median volume diameter NRC = National Research Council p = pressure p o = stagnation pressure pph = pounds per hour psia = force pounds per square inch, absolute RATFac = Research Altitude Test Facility RH = relative humidity, % sec = second TAT or T o = total air temperature T wb = wet bulb temperature based on total air temperature, total pressure and specific humidity TWC m = Total Water Content (g/m 3 ) measured with SEA WCM-2000 multi-wire instrument µm = micrometer (micron)

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This paper describes ongoing research intended to simulate ice accretion in an intercompressor duct bleed slot resulting from the ingestion of altitude ice crystals. The authors have previously shown that ice crystal particle size plays an important role in the ice crystal accretion phenomenon. It was also shown that ice crystal particle size affects the degree of natural melt that occurs for a given aerodynamic condition. The data presented herein decouples the effects of ice particle melt and particle size distribution to generate accretions with the same ratio of freestream liquid-to-total water fraction. The effects of wet bulb temperature and ice particle size on the natural melting of ice crystals are discussed. An ice preservation procedure is followed to allow tracings of the accretion to be taken along the test article. Ice crystal particle size distribution is characterized using a shadowgraphy imaging technique. Finally, the reduction in accretion rate relative to the theoretical maximum rate of surface accretion by ice crystal particles is discussed.The test article simulates a forward facing, inclined endwall bleed slot in a gas turbine compressor as a simplified two-dimensional representation. The geometry, having a surface inclined 20° to the incoming flow, proved to be susceptible to mixed phase ice crystal accretion. Particle size and particularly the large particle tail of the distribution had a significant impact on the magnitude of accretion under mixed phase test conditions for wet bulb temperatures above and below 0°C. The leading edge growth rates were found to be 1/4 to 1/9 of the theoretical growth rate suggesting that erosion, splashing, particle bounce and other loss mechanism rates are significant. The ice tracings were used to estimate an accretion mass for a hypothetical large bypass ratio gas turbine. It was found that approximately 4kg of ice could be generated should the inter-compressor duct be exposed to the conditions tested for 5 minutes. NomenclatureC = centigrade CCD = Charge-Coupled Device D max = maximum diameter of detected particles D vnn = volume diameter, where nn is the percentage of spray volume that contained particles smaller than this diameter FAA = Federal Aviation Administration GTL = Gas Turbine Laboratory IWCi = Ice Water Content injected (g/m 3 ), based on ice mass flow rate and test section volume airflow kPa = kilopascal LE = leading edge LWC i = Liquid Water Content injected (g/m 3 ) via supplemental spray nozzles, based on water flow rate and test section volume airflow LWC m = Liquid Water Content (g/m 3 ) measured with SEA WCM-2000 multi-wire instrument 1 Mach = Mach number MMD = Median Mass Diameter of ice crystals MVD = Median Volume Diameter NIST = National Institute of Standards and Technology NRC = National Research Council p = pressure p o = stagnation pressure PIV = particle image velocimetry pph = pounds per hour psia = force pounds per square inch, absolute RATFac = Research Altitude Test Facility RH = relative humidity, % sec = second TAT or T...

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