Fundamental Ice Crystal Accretion Physics Studies

Abstract

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

Fundamental Study of Mixed-Phase Icing with Application to Ice Crystal Accretion in Aircraft Jet Engines

“…A.10 can often be simplified by assuming /T s ≈ 1 and /T ∞ ≈ 1 to eliminate the temperature ratios, and then = =2 J/kg, and C p =1000 J/kgK to obtain: setting n 1/3, Le=1. 2 …”

Numerical simulation of ice accretion under mixed-phase conditions

“…The temperature of the metal surface was reduced with continual impingement and adherence of ice crystals. Ice accretion occurred when the temperature of the metal surface was less than 0 C. The assumption was confirmed by Fuleki et al [2][3][4][5] who replicated the icing process of ice crystals in a laboratory with an air temperature above the freezing point. When the ice crystals enter the core flow and partially melt, the flow then becomes mixed-phase because the flow includes air, water droplets, and ice crystals.…”

“…The rebounding of ice crystals after breakup does not contribute to icing. Hence, _ m imp,cryremain ¼ 0:0, Q imp,crystal ¼ 0:0, and _ m ice,c can be obtained using equations (8), (5), and (7).…”

Eulerian method for ice crystal icing in turbofan engines

“…The first three of these facilities are capable of simulating ice crystals under various altitude conditions. These upgrades have resulted into a number of experimental studies on glaciated and mixed-phase accretion for various geometries: an aerofoil shape by Struk et al [127], a NACA-0012 aerofoil by Al-Khalil et al [2] and Struk et al [126], a double-wedge aerofoil by Currie et al [23,22] and Struk et al [124,126], a streamlined body with an axi-symmetric hemispherical nose, with a cylindrical nose and with a conical nose by Currie et al [22,24,25], a bleed slot in a compressor stage by Knezevici et al [71,72] and an aerofoil in a compressor transition S-duct by Mason et al [96].…”