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surface water was found to be refrozen gradually in the downstream region beyond the protected area. This is a rather common problem faced by all the thermal-based anti-/deicing systems. A hybrid anti-/ deicing concept by integrating DBD plasma heating near the airfoil leading edge with hydro-/ice-phobic coatings [27] over the airfoil surface may offer a promising solution to this problem, which will be explored in the near future. For the hybrid anti-/deicing system, although DBD plasma actuators will be used to cover the region near the airfoil leading edge, the rest of the airfoil surface will be coated with promising hydro-/ice-phobic materials. Although minimized power inputs were applied to the DBD plasma actuators to effectively delaminate the ice accretion near the airfoil leading edge, runback surface water would be easily removed from the hydro-/ice-phobic airfoil surface by aerodynamic shear forces. Such a hybrid anti-/ deicing strategy is expected to be able to delay/reject ice accretion over the entire airfoil surface at a much lower power cost than the method with massive brute-force heating over the entire airfoil surface. IV. Conclusions An explorative study was conducted to evaluate the effectiveness of leveraging thermal effect induced by dielectric-barrier-discharge (DBD) plasma generation for aircraft icing mitigation. The experimental study was performed in an icing research tunnel available at the Aerospace Engineering Department of Iowa State University. A NACA 0012 airfoil/wing model embedded with two sets of DBD plasma actuators over the airfoil surface was mounted inside the ISU-IRT under typical glaze-/rime-icing conditions pertinent to aircraft inflight icing phenomena. During the experiments, while a high-speed imaging system was used to record the dynamic ice-accretion and transient surface water transport processes over the airfoil surface, an infrared thermal imaging system was also used to map the corresponding surface temperature distributions over the airfoil surface. Based on the side-by-side comparisons of the measurement results (i.e., snapshots of the visualization images and quantitative surface temperature distribu- tions) for the plasma-on case against those of the plasma-off case under the same icing conditions, the effectiveness of using the thermal effects induced by DBD plasma generation for aircraft icing mitigation was evaluated in detail. It was found that, upon the impingement of supercooled water droplets carried by the incoming airflow onto the airfoil surface, ice accretion would take place immediately over the airfoil surface if the embedded DBD plasma actuators were switched off, as expected. As time went by, with more and more supercooled water droplets impinged onto the airfoil surface, the ice layers accumulated over the airfoil surface were found to become thicker and thicker for the plasma-off case. However, if the plasma actuators were turned on T∞ −5°C, and LWC 1.5 g∕m ), the surface temperatures of the entire airfoil model were found to stay above the water frozen temperature (i.e., Tw > 0°C). Due to the thermal effects induced by DBD plasma generation, the supercooled water droplets were found to be heated up, and they formed a layer of warm water film over the airfoil surface instead of being frozen into solid ice. Driven by the boundary-layer airflow over the airfoil surface, the warm liquid water accumulated over the airflow surface was found to run back to further downstream regions, and it shed eventually from the airfoil trailing edge. As a result, the airfoil surface under the typical glaze-ice condition was found to be completely free of ice during the entire ice- accretion experiment. As for a typical rime-icing case (i.e., under the test conditions of U∞ 40 m∕s, T∞ −15°C, and LWC 1.0 g∕m3), although the thermal effects induced by the DBD plasma generation were demonstrated to be effective in preventing ice formation and accretion over the area protected by the DBD plasma actuators, the runback surface water was found to be refrozen gradually in the downstream region beyond the protected area due to at the much colder ambient temperature. This is a rather common problem faced by all the thermal based anti-/deicing systems. A hybrid anti-/deicing concept by integrating DBD plasma heating near the airfoil leading edge with hydrophobic/ice-phobic coatings over the airfoil surface was proposed to address this problem, which will be explored in the near future. It should be noted that, although the present study demonstrated clearly that DBD plasma actuators can be used as a promising anti-/ deicing tool for aircraft icing mitigation by taking advantage of the thermal effects associated with DBD plasma generation, a side-by- side comparative study is planned to evaluate the effectiveness of the plasma-based anti-/deicing strategy (i.e., in the term of the required power consumption for anti-/deicing operation) against that of conventional electrothermal heating methods for aircraft icing mitigation under different icing conditions. More comprehensive studies will also be conducted to elucidate the underlying mechanism pertinent to plasma-based anti-/deicing technology in order to explore/optimize design paradigms for the development of effective and robust anti-/deicing strategies to ensure safer and more efficient operation of aircraft in cold weather. Acknowledgments The research work is partially supported by Iowa Space Grant Consortium Base Program for Aircraft Icing Studies, with Richard Wlezien as the Director. The authors also gratefully acknowledge the support of the National Science Foundation under award numbers CBET-1064196 and CBET-1435590. The technical assistance of Feng Liu of the University of California, Irvine; Jinsheng Cai of Northwestern Polytechnic University; and Cem Kolbakir of Iowa State University is greatly appreciated. References [1] Petty, K. R., and Floyd, C. D. J., “A Statistical Review of Aviation Airframe Icing Accidents in the US,” Proceedings of the 11th Conference on Aviation, Range, and Aerospace, Sec. 11, No. 2, National Transportation Safety Board, Hyannis, MA, Oct. 2004, https:// ams.confex.com/ams/11aram22sls/techprogram/paper_81425.htm [retrieved 20 Oct. 2017]. [2] Gent, R. W., Dart, N. P., and Cansdale, J. T., “Aircraft Icing,” Philosophical Transactions of the Royal Society of London, A: Mathematical, Physical and Engineering Sciences, Vol. 358, No. 1776, 2000, pp. 2873–2911. doi:10.1098/rsta.2000.0689 [3] Liu, Y., Chen, W. L., Bond, L. J., and Hu, H., “An Experimental Study on the Characteristics of Wind-Driven Surface Water Film Flows by Using a Multi-Transducer Ultrasonic Pulse-Echo Technique,” Physics of Fluids, Vol. 29, No. 1, 2017, Paper 012102. doi:10.1063/1.4973398 [4] Bragg, M. B., Broeren, A. P., and Blumenthal, L. A., “Iced-Airfoil Aerodynamics,” Progress in Aerospace Sciences, Vol. 41, No. 5, 2005, pp. 323–362. doi:10.1016/j.paerosci.2005.07.001 [5] Cebeci, T., and Kafyeke, F., “Aircraft Icing,” Annual Review of Fluid Mechanics, Vol. 35, No. 1, 2003, pp. 11–21. doi:10.1146/annurev.fluid.35.101101.161217 [6] Liu, Y., Waldman, R. M., and Hu, H., “An Experimental Investigation on the Unsteady Heat Transfer Process over an Ice Accreting NACA 0012 Airfoil,” 53rd AIAA Aerospace Sciences Meeting, AIAA Paper 2015- 0035, 2015. doi:10.2514/6.2015-0035 [7] Waldman, R. M., and Hu, H., “High-Speed Imaging to Quantify Transient Ice Accretion Process over an Airfoil,” Journal of Aircraft, Vol. 53, No. 2, 2016, pp. 369–377. doi:10.2514/1.C033367 [8] Fortin, G., Laforte, J. L., and Ilinca, A., “Heat and Mass Transfer During Ice Accretion on Aircraft Wings with an Improved Roughness Model,” International Journal of Thermal Sciences, Vol. 45, No. 6, 2006, pp. 595–606. doi:10.1016/j.ijthermalsci.2005.07.006 [9] Rutherford,R.B.,“De-IceandAnti-IceSystemandMethodforAircraft Surfaces,” U.S. Patent No. 6194685 B1, 2001. [10] Thomas, S. K., Cassoni, R. P., and MacArthur, C. D., “Aircraft Anti- Icing and De-Icing Techniques and Modeling,” Journal of Aircraft, Vol. 33, No. 5, 1996, pp. 841–854. doi:10.2514/3.47027 under a typical glaze-ice condition (i.e., U 40 m∕s, 3∞ ZHOU ET AL. 1103 Downloaded by IOWA STATE UNIVERSITY on October 5, 2018 | http://arc.aiaa.org | DOI: 10.2514/1.J056358PDF Image | Utilization of Thermal Effect Induced by Plasma Generation for Aircraft Icing Mitigation
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