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 ...

Due to numerous engine power-loss events associated with high-altitude convective weather, ice accretion within an engine due to ice-crystal ingestion is being investigated. The National Aeronautics and Space Administration (NASA) and the National Research Council (NRC) of Canada are starting to examine the physical mechanisms of ice accretion on surfaces exposed to ice-crystal and mixed-phase conditions. In November 2010, two weeks of testing occurred at the NRC Research Altitude Facility utilizing a single wedge-type airfoil designed to facilitate fundamental studies while retaining critical features of a compressor stator blade or guide vane. The airfoil was placed in the NRC cascade wind tunnel for both aerodynamic and icing tests. Aerodynamic testing showed excellent agreement compared with CFD data on the icing pressure surface and allowed calculation of heat transfer coefficients at various airfoil locations. Icing tests were performed at Mach numbers of 0.2 to 0.3, total pressures from 93 to 45 kPa, and total temperatures from 5 to 15°C. Ice and liquid water contents ranged up to 20 and 3 g/m 3 , respectively. The ice appeared well adhered to the surface in the lowest pressure tests (45 kPa) and, in a particular case, showed continuous leadingedge ice growth to a thickness greater than 15 millimeters in 3 minutes. Such widespread deposits were not observed in the highest pressure tests, where the accretions were limited to a small area around the leading edge. The suction surface was typically ice-free in the tests at high pressure, but not at low pressure. The icing behavior at high and low pressure appeared to be correlated with the wet-bulb temperature, which was estimated to be above 0°C in tests at 93 kPa and below 0°C in tests at lower pressure, the latter enhanced by more evaporative cooling of water. The authors believe that the large ice accretions observed in the low pressure tests would undoubtedly cause the aerodynamic performance of a compressor component such as a stator blade to degrade significantly, and could damage downstream components if shed.https://ntrs.nasa.gov/search.jsp?R=20120004044 2018-05-12T11:53:54+00:00Z

This paper presents results from an initial study of the fundamental physics of ice-crystal ice accretion using the NASA Propulsion Systems Lab (PSL). Ice accretion due to the ingestion of ice-crystals is being attributed to numerous jet-engine power-loss events. The NASA PSL is an altitude jet-engine test facility which has recently added a capability to inject ice particles into the flow. NASA is evaluating whether this facility, in addition to full-engine and motor-driven-rig tests, can be used for more fundamental ice-accretion studies that simulate the different mixed-phase icing conditions along the core flow passage of a turbo-fan engine compressor. The data from such fundamental accretion tests will be used to help develop and validate models of the accretion process. The present study utilized a NACA0012 airfoil. The mixed-phase conditions were generated by partially freezing the liquid-water droplets ejected from the spray bars. This paper presents data regarding (1) the freeze out characteristics of the cloud, (2) changes in aerothermal conditions due to the presence of the cloud, and (3) the ice accretion characteristics observed on the airfoil model. The primary variable in this test was the PSL plenum humidity which was systematically varied for two duct-exit-plane velocities (85 and 135 m/s) as well as two particle size clouds (15 and 50 µm MVDi). The observed clouds ranged from fully glaciated to fully liquid, where the liquid clouds were at least partially supercooled. The air total temperature decreased at the test section when the cloud was activated due to evaporation. The ice accretions observed ranged from sharp arrow-like accretions, characteristic of ice-crystal erosion, to cases with doublehorn shapes, characteristic of supercooled water accretions. NomenclatureA = Area of test section AAI = Advanced Aircraft Icing subproject.

A thermodynamic model is presented to describe possible mechanisms of ice formation on unheated surfaces inside a turbofan engine compression system from fully glaciated ice crystal clouds often formed at high altitude near deep convective weather systems. It is shown from the analysis that generally there could be two distinct types of ice formation: (1) when the "surface freezing fraction" is in the range of 0 to 1, dominated by the freezing of water melt from fully or partially melted ice crystals, the ice structure is formed from accretion with strong adhesion to the surface, and (2) when the "surface melting fraction" is the range of 0 to 1, dominated by the further melting of ice crystals, the ice structure is formed from accumulation of un-melted ice crystals with relatively weak bonding to the surface. The model captures important qualitative trends of the fundamental ice-crystal icing phenomenon reported earlier 1,2 from the research collaboration work by NASA and the National Research Council (NRC) of Canada. Further, preliminary analysis of test data from the 2013 full scale turbofan engine ice crystal icing test 3 conducted in the NASA Glenn Propulsion Systems Laboratory (PSL) has also suggested that (1) both types of ice formation occurred during the test, and (2) the model has captured some important qualitative trend of turning on (or off) the ice crystal ice formation process in the tested engine low pressure compressor (LPC) targeted area under different icing conditions that ultimately would lead to (or suppress) an engine core roll back (RB) event. Nomenclature b= relative heat factor, dimensionless b = modified relative heat factor, dimensionless 0 c = specific ratio of ice particle kinetic heating to latent heat absorbed from melting, dimensionless c p,air = specific heat of air, cal/g K c p,ws = specific heat of water at the surface temperature, cal/g K h c = convective heat-transfer coefficient, cal/s m 2 K h G = gas-phase mass-transfer coefficient, g /s m 2 IWC = ice water content, g/m 3 LWC = liquid water content of melted ice, g/ m 3 MR = ice crystal melt ratio, = LWC t /IWC i , dimensionless M  = local Mach number, dimensionless MMD = ice crystal median mass diameter, m MVD = water droplet median volume diameter, m e m = mass flux of water evaporated per unit time, lbm/ft 2 s imp m = mass flux of ice/liquid-water particle impinged per unit time, lbm/ft 2 s 2 , melt imp m = mass flux of water-melt impinged per unit time, lbm/ft 2 s m 0 = surface melting fraction at stagnation, dimensionless n 0 = surface freezing fraction at stagnation, dimensionless p = pressure, N/m 2 p v,w = the saturation vapor pressure of water in atmosphere, N/m 2 p v,ws= the saturation vapor pressure of water over icing surface, N/m 2 q conv = surface heat loss due to convection, Btu/hr ft 2 q evap = surface heat loss from evaporation, Btu/hr ft 2 q freeze = surface heat gain from release of latent heat of fusion, Btu/hr ft 2 q kinetic = surface heat gain from kinetic energy of ice crystals and water drops, Bt...

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.