Development and commissioning of a linear compressor cascade rig for ice crystal research

This paper describes the commissioning of a linear compressor cascade rig for ice crystal research. The rig is located in an altitude chamber so the test section stagnation pressure, temperature and Mach number can be varied independently. The facility is open-circuit which eliminates the possibility of recirculating ice crystals reentering the test section and modifying the median mass diameter and total water content in time. As this is an innovative facility, the operating procedures and instrumentation used are discussed. Sample flow quality data are presented showing the distribution of velocity, temperature, turbulence intensity and ice water concentration in the test section. The control and repeatability of experimental parameters is also discussed. Although the rig was designed to investigate the ice crystal phenomenon in an environment representative of a compressor stator row, the test section can be reconfigured to assess the performance of aircraft air data sensors as well.Peer reviewed: YesNRC publication: Ye

Altitude scaling of ice crystal accretion

This paper describes experiments performed in an altitude chamber at the National Research Council 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 accretion-susceptible 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 45\u3bc, some of the scaling tests were repeated with larger particles, which produced smaller accretions. \ua9 2013 by Her Majesty the Queen in Right of Canada. Published by the American Institute of Aeronautics and Astronautics.Peer reviewed: YesNRC publication: Ye

Particle size effects on ice crystal accretion - Part II

This paper describes ongoing research intended to simulate ice accretion in an inter-compressor 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\ub0 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\ub0C. 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. \ua9 2013 by Her Majesty the Queen in Right of Canada. Published by the American Institute of Aeronautics and Astronautics.Peer reviewed: YesNRC publication: Ye