A Hybrid System for Ice Protection and Detection

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A Hybrid System for Ice Protection and Detection


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A Hybrid System for Ice Protection and Detection Tobias Strobl (1), Robert Adam (2), Ricardo Entz (3) 1 : Airbus Group Innovations, Munich, 81663, Germany, Tobias.Strobl@airbus.com 2 : Airbus Group Innovations, Robert.Adam@airbus.com, 3 : Airbus Group Innovations, Ricardo.Entz@airbus.com Abstract Aircraft icing is considered a serious weather hazard during flight. Against the background of a more- electric aircraft, electro-thermal and -mechanical systems for ice protection are well-suited to remove in-flight ice accretions from aircraft components. This effort intends to investigate the performance of a hybrid ice protection system for a small-scale configuration in a laboratory-size icing wind tunnel. The hybrid ice protection system is composed of a slender thermo-electric heating wire at the stagnation line, piezoelectric actuators in the unheated aft regions and a superhydrophobic surface with low ice adhesion properties, which is applied in the leading edge area of the airfoil. The hybrid system is analyzed regarding its efficacy for shedding minimum thicknesses in ice using a laser-scanning system. In addition, the extent to which the system is able to detect whether ice is accreted on the surface is also examined. Introduction Ice can be considered to be a main threat to aviation. Even slight deposits of ice on the wing, empennage or instruments can adversely affect the aerodynamic performance and control of an aircraft, i.e., lift decreases while drag simultaneously increases and, in a worst case scenario, control of the aircraft may be entirely lost. 1-3 To counteract ice accretion, state- of-the-art ice protection systems for e.g. the wing are based on using bleed air to melt the ice in the area of the leading edge, which is the critical area for droplet impingement and ice accretion, respectively. Primarily for reasons related to energy consumption, research and development efforts are focused on approaches to replace existing bleed air systems by e.g. using electro-thermal heater blankets. 3,4 This effort investigates the performance of a hybrid approach for aircraft ice protection. Two electrical subsystems, i.e., a thermo-electric heating wire and an electro-mechanical system based on piezoelectric multilayer actuators, are therefore installed in the hollow leading edge of a NACA 0012 airfoil with a chord length of 177.8 mm. 5 In addition, for reasons related to ice adhesion reduction, a water- and ice- repellent surface is applied in the leading edge area of the airfoil. 5,6 The system efficacy for ice removal using the piezoelectric actuators and, in particular, for shedding ice layers with low thickness values, is evaluated in a laboratory-scale icing wind tunnel facility using a laser scanning system. 7 In addition, the capability of the piezoelectric actuators for detecting whether ice is accreted on the surface of the small-scale airfoil is also examined. Calibration set-up for ice thickness measurement Calibration of the laser scanning system is performed in the icing wind tunnel by direct measurement of the thickness of the ice that is accreted on a 150 mm chord NACA 0012 airfoil using a transparent baffle with millimeter-scale, as Fig. 1 a) shows, and a digital single-lens reflex (DSLR) camera set up to provide a lateral view on the airfoil, which is illustrated in Fig. 1 b). Fig. 1: a) NACA 0012 airfoil with a transparent baffle and, b) laser scanning system with a laser diode and detector (1), and a digital single-lens reflex (DSLR) camera (2) The laser scanning system is installed on top of the wind tunnel test section to cover the chordwise dimension of the 150 mm chord NACA 0012 airfoil. The measurement values of the thickness of the ice layers using the DSLR camera are used to adjust the results of the laser scanning system, as Fig. 2 depicts, since the determination of the ice thickness on the 177.8 mm chord NACA 0012 airfoil with the internally attached hybrid ice protection system (HIPS) will be performed without the baffles and the DSLR camera. Glaze ice, mixed-ice and rime ice conditions are examined for calibration at 90 m/s and 120 m/s. The corresponding total and static temperatures of the airstream are listed in Table 1. Fig. 2: Top-view of the wind tunnel test section with the laser scanning system during a glaze ice accretion on the 150 mm NACA 0012 airfoil with the attached transparent baffle. Test run Ice type Ttot [°C] Tst [°C] Vair [m/s] 1 Glaze ice 0 -4,03 90 2 Glaze ice -5 -9,03 90 3 Mixed ice -10 -14,03 90 4 Rime ice -15 -19,03 90 5 Glaze ice 0 -7,16 120 6 Glaze ice -5 -12,16 120 7 Mixed ice -10 -17,16 120 8 Rime ice -15 -22,16 120 Table 1: Test conditions for the ice thickness calibration measurements Laser scanning method for the ice thickness measurement During operation of the HIPS the determination of the thickness of the ice layer is performed using the laser scanning system and the data set from the calibration measurements. The thermo-electric heating wire operates in a running-wet anti-icing mode to continuously keep the area around the stagnation line free from ice accretion, whereas ice accumulates in the unheated aft regions of the airfoil on the upper and lower sides, where the piezoelectric actuators are positioned inside the hollow leading edge, as Fig. 3 illustrates. The thickness values of the partitioned ice deposits are evaluated with regard to the minimum detectable thickness of the ice with the laser scanning system and the minimum thickness of the ice that can be reliably shed using the piezoelectric actuators. Prior to the excitation with the piezoelectric actuators, Fig. 3 shows a lateral image of the upper ice deposit that is accreted in the unheated aft region of the airfoil at glaze ice conditions and at a total air temperature of approximately 0 °C. The thickness of the ice deposit in Fig. 3 ranges between 0.58 and 1.15 mm. Fig. 3: NACA 0012 airfoil for calibration measurement, and b) top-view on the test section with the laser scanning system in operation. The disruption of the bond between the airfoil surface and the ice is initiated when it comes to application of voltage to the piezoelectric actuators. The actuators are periodically excited using a frequency sweep between 3 and 5 kHz with a total sweep time of 3 seconds. The sweep intends to excite the airfoil and, in particular, the leading edge area with the ice accretion, at its resonance frequency for a maximum in surface deformation. Hence, due to the surface deformation performed by the electro-mechanical subsystem, the upper and lower ice deposits shown in Fig. 3 are entirely shed from the airfoil surface. The full paper will present an entire study of ice shedding using the hybrid ice protection system, i.e., a detailed study of the different icing conditions given in Table 1. The minimum thickness in ice that can reliably be shed by the system is the main objective of this effort. In addition, the full paper will also include a comparison between the HIPS and a reference system, which is an identical NACA 0012 airfoil with an internally attached thermo-electric heating wire and the piezoelectric actuators. However, it is essential to notice that for the reference system, the water- and ice-repellent surface is replaced by an aluminum surface that is pre-treated by a tartaric sulphuric anodizing process and then coated with a conventional corrosion inhibiting primer of type Cytec BR 127. The aim of the comparison to the reference system is to quantify the beneficial effect of the superhydrophobic and icephobic coating used for the hybrid ice protection system. 5,6 Ice detection measurement Besides the ice removal efficacy of the HIPS, the system can also be used for reasons related to ice detection due to the fact that any arbitrary ice accretion on the surface will alter the resonance frequency and damping behavior of the airfoil. 5 Prior to the accretion of ice, a reference measurement of the clean airfoil has to be performed. The green lines in Figs. 4 a) and 4 b) show the reference values for the amplitude and the phase of the airfoil without ice accretion. For the detection of potential ice accumulations on the surface, the airfoil is stimulated with a recurring low level frequency sweep between 3 and 5 kHz. for a. The red and blue lines in Figs. 4 a) and 4 b) illustrate the shift of the amplitude and the phase of the reactance to higher values for a 5s and 45 s ice accretion, respectively. Hence, it becomes obvious that the piezoelectric actuators reliably indicate whether ice has formed on the surface. Fig. 4: a) Amplitude of the reactance, and b) phase of the reactance for the clean airfoil and the identical airfoil with a 5s and 45s ice accretion, respectively. Conclusions This effort investigates the efficacy of a hybrid ice protection system regarding the removal of very low thicknesses of ice that forms on the surface of an airfoil, and, in particular, in the unheated regions of the airfoil. The ice removal is performed by surface deformation due to the piezoelectric actuators. During the process of ice removal, a laser scanning system is used to detect the extent to which the system is capable of removing minimum thicknesses of ice. The full paper will contain a detailed description of the ice removal efficacy of the HIPS when the airfoil is applied to conditions similar to realistic in-flight icing. The full paper will also include the detailed analyses for assessing how the piezoelectric actuators are capable of detecting whether ice accretes on the surface of the airfoil. References 1 Civil Aviation Authority. (2000, June 14). Aircraft Icing Handbook. Retrieved April 09, 2011, from http://www.caa.govt.nz/search/query.asp. 2 Federal Aviation Administration. (2007, December 31). Advisory Circular AC 91-74A - Pilot Guide: Flight in Icing Conditions. Retrieved April 09, 2011, from http://rgl.faa.gov/REGULATORY_AND_ GUIDANCE_LIBRARY%5CRGADVISORYCIRCULA R.NSF/0/4C8192BB0B733862862573D2005E7151? OpenDocument. 3 Airbus Industrie (2000). Getting to Grips with Cold Weather Conditions. A Flight Operations View; Flight Operations Support - Customer Services Directorate. AI/ST-F 945.9843/99. Ref: AI/SR A007-01/00. 4 J. Fraga, AERO_Q407: 787 No-Bleed Systems: Saving Fuel and Enhancing Operational Efficiencies, http://www.boeing.com/commercial/aeromagazine/arti cles/qtr_4_07/AERO_Q407.pdf. 5 T. Strobl, S. Storm, D. Thompson, M. Hornung, Feasibility Study of a Hybrid Ice Protection System, in: 6th AIAA Atmospheric and Space Environments Conference, American Institute of Aeronautics and Astronautics, 2014. 6 T. Strobl, S. Storm, M. Kolb, J. Haag, M. Hornung, Development of a Hybrid Ice Protection System Based on Nanostructured Hydrophobic Surfaces, 29th Congress of the International Council of the Aeronautical Sciences, (submitted for publication). 7 T. Strobl, D. Raps, M. Hornung, Evaluation of Roughness Effects on Ice Adhesion, in: 5th AIAA Atmospheric and Space Environments Conference, American Institute of Aeronautics and Astronautics, 2013.