UNIVERSITY OF NAPLES “FEDERICO II” PhD course in Aerospace, Naval and Quality Engineering PhD Thesis in Aerospace Engineering “ELECTRICALLY HEATED COMPOSITE LEADING EDGES FOR AIRCRAFT ANTI-ICING APPLICATIONS” by Francesco De Rosa 2010 To my girlfriend Tiziana for her patience and understanding precious and rare human virtues University of Naples Federico II Department of Aerospace Engineering DIAS PhD Thesis in Aerospace Engineering Author: F. De Rosa Tutor: Prof. G.P. Russo PhD course in Aerospace, Naval and Quality Engineering XXIII PhD course in Aerospace Engineering, 2008-2010 PhD course coordinator: Prof. A. Moccia ___________________________________________________________________________ Francesco De Rosa - Electrically Heated Composite Leading Edges for Aircraft Anti-Icing Applications 2 Abstract An investigation was conducted in the Aerospace Engineering Department (DIAS) at Federico II University of Naples aiming to evaluate the feasibility and the performance of an electrically heated composite leading edge for anti-icing and de-icing applications. A 283 [mm] chord NACA0012 airfoil prototype was designed, manufactured and equipped with an High Temperature composite leading edge with embedded Ni-Cr heating element. The heating element was fed by a DC power supply unit and the average power densities supplied to the leading edge were ranging 1.0 to 30.0 [kW m-2]. The present investigation focused on thermal tests experimentally performed under fixed icing conditions with zero AOA, Mach=0.2, total temperature of -20 [°C], liquid water content LWC=0.6 [g m-3] and average mean volume droplet diameter MVD=35 [µm]. These fixed conditions represented the top icing performance of the Icing Flow Facility (IFF) available at DIAS and therefore it has represented the “sizing design case” for the tested prototype. An analytical model has been also developed both for the preliminary sizing and test guidance. Running wet and fully evaporative functional modes have been verified both analytically and experimentally with reasonable agreement. A room temperature thermal endurance test has been run for 104 cycles with max thermal load representative of 1.5 times the max temperature experienced within the leading edge in fully evaporative conditions aiming to verify the integrity of the composite laminate after the imposed thermal stress through micrographic inspection. The achieved results, despite obtained under limited icing conditions imposed by the IFF wind tunnel, showed great potentialities for the proposed Icing Protection System named EHCLE (Electrical Heated Composite Leading Edge) which has been constantly working below 60% of its maximum operative temperatures under the given icing conditions and the explored power densities. This potentiality justify the need for future development in a larger scale under more severe icing condition for a final assessment about the applicability of such Icing Protection System to real aircrafts. Key words: anti-icing, de-icing, High Temperature Composite, EHCLE, IPS ___________________________________________________________________________ Francesco De Rosa - Electrically Heated Composite Leading Edges for Aircraft Anti-Icing Applications 3 Acknowledgements I would first like to thank my Tutor and advisor Prof. G.P. Russo for his guidance. His expertise during the numerous problems encountered in this study were invaluable. I wish to thank Dr. A. Esposito for his support and availability night and day, his extensive expertise in experimental methods and techniques has been essential to the project. I also wish to thank all the other members of the team which has been working for more than two years to make this research feasible and among them a special gratitude goes to V. Caso and F. Parente for helping to solve experimental and numerical problems. This work was supported by the Department of Aerospace Engineering DIAS and therefore a special thanks goes to the DIAS Director Prof. F. Marulo which believed in the project and made the laboratory available. During the years working at the University of Naples Aerodynamics Laboratory, I had the pleasure of working with many PhD, graduate and undergraduate students. I would like to thank all of them. ___________________________________________________________________________ Francesco De Rosa - Electrically Heated Composite Leading Edges for Aircraft Anti-Icing Applications 4 Table of Contents Abstract .......................................................................................................................................3 Acknowledgements.....................................................................................................................4 Table of Contents........................................................................................................................5 List of Figures .............................................................................................................................7 List of Tables ............................................................................................................................10 Nomenclature............................................................................................................................11 1 Introduction...........................................................................................................................13 1.1 Research objectives............................................................................................................15 1.2 Review of Icing Literature .................................................................................................15 1.2.1 Droplet Classification .....................................................................................................16 1.2.2 Aircraft Icing Risks.........................................................................................................17 1.2.3 Ice Shapes .......................................................................................................................18 1.2.4 Impingement area considerations ...................................................................................19 1.2.5 Flowfield around an iced Airfoil.....................................................................................21 1.2.6 Effects of Ice-Shape Height ............................................................................................22 1.2.7 Effects of Ice-Shape Geometry.......................................................................................22 1.2.8 Reynolds Number Effects ...............................................................................................23 1.2.9 Effect of Ice Shape Location...........................................................................................23 1.2.10 Effects on High Lift and Control Surfaces ...................................................................24 1.3 Definitions..........................................................................................................................24 1.3.1 Glaze ice (Clear Ice) .......................................................................................................24 1.3.2 Rime Ice ..........................................................................................................................25 1.3.3 Mixed Ice ........................................................................................................................25 1.3.4 Hoar Frost .......................................................................................................................26 1.3.5 Ice Accretion Mechanism ...............................................................................................26 1.3.6 Double Horn Shape.........................................................................................................26 1.3.7 Ram Effect ......................................................................................................................27 1.3.8 Run Back Ice and Shear Forces ......................................................................................27 1.3.9 Sublimation.....................................................................................................................27 1.3.10 Importance of Airspeed.................................................................................................28 1.3.11 Cloud types ...................................................................................................................28 1.3.12 Liquid Water Content in Clouds (LWC) ......................................................................29 1.3.13 Ice collection efficiency EM and water interception rate MT ........................................31 1.3.14 Icing Characteristics......................................................................................................32 1.3.15 Super Cooled Drizzle Drops .........................................................................................32 1.3.16 Icing Certification .........................................................................................................33 1.3.17 Icing Severity Classification .........................................................................................35 1.3.18 Supercooled Large Droplet (SLD)................................................................................37 1.4 Review of Anti-icing and De-icing Systems .....................................................................38