PHYSICS-BASED SHAPE EVOLUTION, TRAJECTORY AND SURFACE MASS AND ENERGY MODEL OF MIXED-PHASE ICING
Open Access
- Author:
- Yan, Sihong
- Graduate Program:
- Aerospace Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 07, 2021
- Committee Members:
- Robert Kunz, Outside Unit & Field Member
Jose Palacios, Chair & Dissertation Advisor
Cengiz Camci, Major Field Member
Michael Kinzel, Major Field Member
Amy Pritchett, Program Head/Chair - Keywords:
- Aircraft Icing
Multiphase Flow
Wind Tunnel Experiment
Melting Process of Ice Crystals - Abstract:
- The in-flight engine icing is a threat to the aviation safety. The high-altitude ice crystals are inhaled by the engine. The temperature variation inside the engine melts the ice crystals. The partially-melted ice crystals freeze on the housing and the stators of the engine. The ice accretion affects the performance of the engine and potentially lead to severe incidents including the roll-back and the surge in the engine. The National Research Council at Canada conducted a series of crystal icing tests in the high-altitude icing wind tunnel and generated a database of ice shapes and accretion rates for crystal icing. The test in the NRC altitude wind tunnel used a mixture of ice crystals and water droplets. Several models were developed to duplicate the icing results from the NRC test, including a comprehensive model from the ONERA. The model adopts an empirical erosion model and overpredicts the ice accretion up to 31.6 % when the percentage melting of the cloud is over 16%. In this study, a physics-based model is established to study the mechanism of crystal icing on a temperature-controlled surface. The study presented a two-fold approach combining physics-based models and experiments. The physics-based models are focused on the trajectory of non-spherical crystals and the heat and mass balance on the icing surface. The modeling efforts were combined with two experiments, a single crystal experiment, and an ice accretion test in the Pennsylvania State University Icing Wind Tunnel (PSU-IWT). The objective of the research is to develop a physics-based model including the shape evolution of a melting crystal, the trajectory of such crystals and the ice accretion model. The single crystal test rig features an ultrasonic levitator and the luminescent quantification of the percentage melting. The single crystal was levitated and melted under the natural or forced convection. The sphericity variation during the melting process was visualized. The luminescent dye, Rhodamine B was added to the droplet to show the percentage melting. The experiment shows that the shape evolution of a melting crystal can be divided into two sections. The first stage is when the ice core is exposed to the surrounding air. The second stage is when the ice core is fully engulfed by the water layer. The crystals turn fully spherical when the critical percentage melting is reached. The critical percentage, 62.2% is derived from a surface tension model and the value is independent on the diameter of crystals. A total of 17 melting tests were conducted on crystals. The average critical percentage value is 68.6% and the standard deviation is 6.9%. The crystals were melted in the PSU-IWT by a temperature-controlled heating duct. The temperature of the airfoil is controlled and monitored. The test conditions are the combination of two duct temperatures (2.5℃ and 7.5℃) and three surface temperatures (0℃, -5℃ and -10℃). The process of particle melting inside the heating duct is solved by a combined model of the heat and mass exchange on the ice crystal and the trajectory equation. The developed sphericity model is used to calculate the sphericity and the heat and mass transfer coefficient. The novel ice accretion model combines the energy and mass balance on the surface into one integrated model. Based on the balance, there are 3 types of icing regimes. The first is the rime regime when the crystals freeze on the surface instantly. The second regime is the glaze regime where the unfrozen water forms a layer of runback water. The third mode is the wet regime where the ice content of the impinging icing cloud fully melts. The wet regime leads to negative ice growth rates. A new geometric ice accretion model is developed to reconstruct the new ice surface. The ice accretion model is verified by the low-speed test in the PSU-IWT. The average discrepancy of the ice thickness at the leading edge is 10.2%. A special ice shape, the sharp ice cone was only observed in crystal icing. In the ONERA’s model, the ice cone was achieved with the erosion model. A new hypothesis is raised in this study. The ice cone is the result of the convective heating. The 11.2% melted icing cloud are manually injected into two freezing air temperatures, 0 ℃ and -10℃. The ice shapes in both cases have blunt leading edges. The ice horns are common ice shapes in the droplet icing when the cooling capacity of the inflow is low. When the inflow temperatures declines, the ice horns disappear. Significant ice horns grow in the 0℃ simulation and are not present in the -10℃ case. The parametric study shows that the ice cones are directly related to the warm environment for crystal icing.