This paper describes experiments performed in an altitude chamber at the NationalResearch Council of Canada (NRC) as the first phase of a joint NRC/NASA program investigating ice crystal accretion in aero engines. The principal objective was to explore the effect of wet bulb temperature T wb (dependent on air temperature, humidity and pressure) on accretion behavior, since preliminary results published in an earlier paper indicated that well-adhered accretions are only possible at T wb <0°C, when water in an impinging mixedphase flow can freeze to a surface. To assess the accretion sensitivity to T wb , the symmetrical airfoil used in the previous work was tested at pressures of 44.8 kPa and 93kPa, usually at 0.25 Mach number, over a range of freestream liquid water and ice water concentrations, total air temperatures and humidity levels. T wb was typically maintained at +2°C or -2°C, based on dry total conditions (i.e. without ice or water injection). Total air temperature was >0°C in all tests. The limited test results confirmed that accretion behavior is very sensitive to T wb , which is in turn strongly related to pressure since evaporative cooling increases with decreasing pressure. Humidity and total temperature did not appear to have an independent effect on accretion behavior. Accretions, often resembling glaze ice, formed at T wb <0°C, when freestream water would freeze on the test airfoil without ice crystals present in the freestream. At T wb >0°C ice deposits were observed to be slushy, poorly adhered and shed frequently. The size of such deposits appeared to be a non-linear function of the freestream ice water content (IWC), becoming much larger at high IWC. NomenclatureAOA = airfoil angle of attack (°), positive for nose up C p = specific heat D = diffusion coefficient of water vapor in air h c , h m = heat, mass transfer coefficient k = thermal conductivity 1 2 L evap = latent heat of vaporization of water Le = Lewis number (= Pr/Sc) LE = wedge airfoil leading edge IW LW = mass flux C = Ice Water Content (g/m 3 ) C = Liquid Water Content (g/m 3 ) M = Mach number M wt = molecular weight MMD = median mass diameter of ice particles, micrometers NASA = National Aeronautics and Space Administration NRC = National Research Council of Canada Nu = Nusselt number (= h c x/k) p = pressure P P = heat flux a = Pascal (N/m 2 ) r = Prandtl number (= µC p /k) RATFac = Research Altitude Test Facility Re = Reynolds number (= ρUx/µ) RH = relative humidity, % R u = universal gas constant Sc = Schmidt number (= µ/ρD) SH = specific humidity (mass of water vapor/unit mass dry air) t = ice thickness T = temperature TWC = Total Water Content (= IWC + LWC) U = velocity x = distance (length) µ = dynamic viscosity ρ = density ρ acc = accretion density (≈( IWC* ρ ice + LWC* ρ liquid )/TWC, for ice and liquid densities ρ ice and ρ liquid respectively) Subscripts conv = convective evap = evaporative i = injected with the ice grinder or water spray nozzles. Ice or water mass flowrate divided by tunnel air volumetric flowrate to ...

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...

Here we report on the application of non-axisymmetric endwall contouring to mitigate the endwall losses of one conventional- and two high-lift low-pressure turbine airfoil designs. The design methodology presented combines a gradient-based optimization algorithm with a three-dimensional CFD flow solver to systematically vary a free-form parameterization of the endwall. The ability of the CFD solver employed in this work to predict endwall loss modifications resulting from non-axisymmetric contouring is demonstrated with previously published data. Based on the validated trend accuracy of the solver for predicting the effects of endwall contouring, the magnitude of predicted viscous losses forms the objective function for the endwall design methodology. This system has subsequently been employed to optimize contours for the conventional-lift Pack B and high-lift Pack D-F and Pack D-A low-pressure turbine airfoil designs. Comparisons between the predicted and measured loss benefits associated with the contouring for Pack D-F design are shown to be in reasonable agreement. Additionally, the predictions and data demonstrate that the Pack D-F endwall contour is effective at reducing losses primarily associated with the passage vortex. However, some deficiencies in predictive capabilities demonstrate here highlight the need for a better understanding of the physics of endwall loss-generation and improved predictive capabilities. More detailed analysis of the contouring results for the Pack B design is presented in a companion paper (Knesevici et al. [1]).

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This paper describes preparation for ice-crystal icing scaling work utilizing the Cascade rig at the National Research Council (NRC) of Canada's Research Altitude Test Facility (RATFac). Tests supporting this work and continuing the collaboration between National Aeronautics and Space Administration (NASA) and NRC on ice-crystal icing took place between March 26 and April 11, 2012. The focus was on several aspects but emphasized characterization of the RATFac cloud including watercontent and test-section uniformity as well as particle-size measurements. Water content measurements utilized the Science Engineering Associates (SEA) Multi-Element probe while cloud uniformity measurements used light scattering from particles passing through a laser sheet. Finally, particle sizespectra measurements used two developmental shadowgraph systems. Details of these measurements as well as selected results are presented. An analysis algorithm is presented that interprets mixed-phase measurements from the SEA probe using calibrations from individual water and ice clouds. The analysis is applied to one mixed-phase data set generated with a glaciated cloud combined with supplemental water. The test section temperature was below freezing to prevent the natural melting of the ice crystals. The analysis algorithm relies on the measurement of test-section humidity to account for cloud evaporation. Results of the cloud-uniformity measurements using scattered light suggest that the measured intensity is a good first-order measurement of concentration, independent of the water phase. Steeper intensity gradients across the test section are observed with increasing ice-water content. For particle-size measurements, both shadowgraphy methods provide high-quality images of the particles. These images will be processed to establish particle-size distributions and morphology characteristics. The results from this work will help guide future ice-crystal icing research including scaling studies.