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.

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This paper describes the development of a numerical model that couples the thermal interaction between ice particles, water droplets, and the flowing gas of an icing wind tunnel for simulation of NASA Glenn Research Center's Propulsion Systems Laboratory (PSL). The ultimate goal of the model is to better understand the complex interactions between the test parameters and have greater confidence in the conditions at the test section of the PSL tunnel. The model attempts to explain the observed changes in test conditions by coupling the conservation of mass and energy equations for both the cloud particles and flowing gas mass. The model uses isentropic relations to relate gas temperature, velocity, density and pressure with respect to the PSL geometry. Measurements were taken at the PSL during wind tunnel tests simulating ice-crystal and mixed-phase icing that relate to ice accretions within turbofan engines in May 2015. The model was compared to experimentally measured values, where test conditions varied gas temperature, pressure, velocity and humidity levels, as well as the cloud total water content, particle initial temperature, and particle size distribution. Wet-bulb temperatures were generally within a few degrees of freezing. The model showed good agreement with experimentally measured values, to within approximately 30% of the measured change in gas temperature and humidity at the tunnel test section. The model did reasonably well in predicting melt content (liquid mass to total mass) at the test section, especially for clouds with larger particle sizes. In addition, the model predicted particle size at the tunnel exit with good agreement, however, the comparison was limited to clouds consisting of a small particle size distribution. One of the key findings from this work is that there was a nearly constant but slight increase in total wet-bulb temperature when the spray cloud was activated for every test and simulation. In addition, the total wet-bulb temperature in the tunnel plenum was a large factor in determining cloud phase.

The Icing Research Tunnel at NASA Glenn has recently switched from using the Icing Blade to using the SEA Multi-Element Sensor (also known as the multi-wire) for its calibration of cloud liquid water content. In order to peform this transition, tests were completed to compare the Multi-Element Sensor to the Icing Blade, particularly with respect to liquid water content, airspeed, and drop size. The two instruments were found to compare well for the majority of Appendix C conditions. However, it was discovered that the Icing Blade undermeasures when the conditions approach the Ludlam Limit. This paper also describes data processing procedures for the Multi-Element Sensor in the IRT, including collision efficiency corrections, mounting underneath a splitter plate, and correcting for a jump in the compensation wire power. Further data is presented to describe the repeatability of the IRT with the Multi-Element Sensor, health-monitoring checks for the instrument, and a sensingelement configuration comparison. Ultimately these tests showed that in the IRT, the multiwire is a better instrument for measuring cloud liquid water content than the blade.

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