Experimental Investigations on Transient Surface Water Transport and Ice Accreting Processes Pertinent to Aircraft Icing Phenomena
Leonard J. Bond
In the present study, an multi-transducer (sparse array) ultrasonic pulse-echo (MTUPE) technique was developed to quantify the transient surface behaviors of the water film flow driven by boundary layer airflow. The instantaneous surface waves riding on the free surface of the water film flow were characterized based on the measured time series of the water film thickness. Based on the time expansions of the measured thickness profiles of the surface water film flow, a instability transition, from periodical two-dimensional waves to pebbled waves of an obviously non-periodic nature, was observed. Then, the temporally-resolved spatial wave structures in the wind-driven water film flow were reconstructed, which provide more details of the surface morphologies and evolutions of the surface waves in the wind-driven water film flow.
A strategy, based on the use of frequency dependent ultrasonic attenuation, was investigated that has the potential to characterize and differentiate between different types of ice that can form on aircraft during winter operations. The measurement methodology and system were validated using the data for acoustic attenuation in water. The data for two types of ice, rime-like and glaze-like, are in agreement with results from previous measurements. There is a significant difference seen in the ultrasonic attenuation characteristics between the two types of ice. It would appear that there is potential to add attenuation data to on-aircraft ice detection systems which could then potentially enable ice-type specific based de-icing to be implemented. Such optimized de-icing could have a potential for reducing winter weather operational costs, and ensure safety is maintained, or even improved.
A comprehensive experimental study was also conducted to quantify the transient surface water transport and dynamic ice accreting process over a wing surface at different icing conditions. The experiments were conducted in the Icing Research Tunnel available at Iowa State University (ISU-IRT). While the transient behaviors of the surface water transport over an NACA 23012 airfoil with realistic initial ice roughness at the airfoil leading edge were investigated using an innovative digital image projection-correlation (DIPC) technique, the unsteady heat transfer and phase changing processes under different icing conditions were examined in details based on the measured surface temperature maps over the ice accreting surfaces by using an infrared thermal imaging system. The objective of this study is to elucidate the underlying physics of surface water transport and ice accretion to improve our understanding of the important microphysical processes pertinent to aircraft icing phenomena to develop more effective and robust anti-/de-icing strategies to ensure safer and more efficient aircraft operations in cold weather.