Ducted Fan Aerodynamics and Modeling, with Applications of Steady and Synthetic Jet Flow Control Osgar John Ohanian III Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Mechanical Engineering Daniel J. Inman, Committee Chair Kevin B. Kochersberger Andrew J. Kurdila William H. Mason Sam B. Wilson May 4th, 2011 Blacksburg, VA Keywords: ducted fan, shrouded propeller, synthetic jets, flow control, aerodynamic modeling, non-dimensional, unmanned aerial vehicle, micro air vehicle Copyright 2011, Osgar John Ohanian III Ducted Fan Aerodynamics and Modeling, with Applications of Steady and Synthetic Jet Flow Control Osgar John Ohanian III ABSTRACT Ducted fan vehicles possess a superior ability to maximize payload capacity while minimizing vehicle size. Their ability to both hover and fly at high speed is a key advantage for information-gathering missions, particularly when close proximity to a target is essential. However, the ducted fans aerodynamic characteristics pose difficulties for stable vehicle flight and therefore require complex control algorithms. In particular, they exhibit a large nose-up pitching moment during wind gusts and when transitioning from hover to forward flight. Understanding ducted fan aerodynamic behavior and how it can be altered through flow control techniques are the two prime objectives of this work. This dissertation provides a new paradigm for modeling the ducted fans nonlinear behavior and new methods for changing the duct aerodynamics using active flow control. Steady and piezoelectric synthetic jet blowing are employed in the flow control concepts and are compared. The new aerodynamic model captures the nonlinear characteristics of the force, moment, and power data for a ducted fan, while representing these terms in a set of simple equations. The model attains excellent agreement with current and legacy experimental data using twelve non- dimensional constants. Synthetic jet actuators (SJA) have potential for use in flow control applications in UAVs with limited size, weight, and power budgets. Piezoelectric SJAs for a ducted fan vehicle were developed through two rounds of experimental designs. The final SJA design attained peak jet velocities in the range of 225 ft/sec (69 m/s) for a 0.03 x 0.80 rectangular slot. To reduce the magnitude of the nose-up pitching moment in cross-winds, two flow control concepts were explored: flow separation control at the duct lip, and flow turning at the duct trailing edge using a Coandă surface. Both concepts were experimentally proven to be successful. Synthetic jets and steady jets were capable of modifying the ducted fan flow to reduce pitching moment, but some cases required high values of steady blowing to create significant responses. Triggering leading edge separation on the duct lip was one application where synthetic jets showed comparable performance to steady jets operating at a blowing coefficient an order of magnitude higher. Acknowledgements Trust in the Lord with all your heart, and lean not on your own understanding, in all you ways acknowledge Him, and He shall direct your paths. Proverbs 3:5-6 Delight yourself in the Lord, and He will give you the desires of your heart. Psalm 37:4 I am the vine, you are the branches. He who abides in Me, and I in him, bears much fruit; for without Me you can do nothing. -Jesus speaking in John 15:5 First and foremost, I would like to thank my loving Creator for making me a curious being who loves to explore His creation and for giving me the opportunity to write this dissertation. Without Him, I can do nothing. Next, I would like to thank my supportive and loving wife, Robin, who has made this arduous journey much more pleasant. Her love and helpful spirit have motivated me to achievements beyond my own expectations. To my children, Ansley, Caleb, Jacob, and Charlotte, thank you for brightening my days when I was uncertain whether I would ever finish, and for your patience when Daddy was busy. I hope to pass on to you my life-long love of learning and exploration of Gods creation. I would like to thank my dad, John, for being a role model in godliness, work ethic, integrity, and care for others. I cant imagine what I would be without your loving guidance over the course of my life. I would like to thank my mom, Mary, for her spontaneous nature, love of people, and appreciation for education. Mom, I love you, and I couldnt have done this without you. For my stepmom, Kim, I wish I could have finished this while you were here, but I know you are cheering me on from heaven. I am rejoicing for your freedom from suffering, and look forward to joining you at the celebration banquet table some day. I would like to thank my advisor, Dr. Dan Inman, for accepting this unconventional Ph.D. student, never losing faith that I would finish, and iii encouraging me all along the way. I have learned more from you than you probably realize. I would like to thank my committee, which includes Dr. Kevin Kochersberger, Dr. Bill Mason, Dr. Andrew Kurdila, and the Right Reverend of the STOVL Faithful, Sam Wilson. Your time and service is sincerely appreciated, and your insights and input to my work have been valuable. To all of my colleagues at AVID LLC, I owe great thanks for their encouragement, helpful collaboration, and creative ideas. Specifically I would like to thank Paul Gelhausen for allowing me the opportunity to pursue a PhD while working full time and supporting me along the way. Now I can get back to work. I would also like to thank all the team members on my SBIR project that contributed to the larger research effort in one way or another. From AVID: Etan Karni, for helping in almost every aspect of the project; Kelly Londenberg, for his CFD work; Adam Entsminger, for his design insights; Chris Hickling, for all the CAD work; Brandon Stiltner, for help with simulations; Chris Olien, for help with experiments; Ignacio Guerrero, for help in vehicle sizing and design; Andy Turnbull, for help with fan designs; Dr. Andy Ko for his general insights; Scott Helsing, for his program management input; and Seth Taylor, for his aerodynamic modeling in Phase I. From Virginia Tech: Onur Bilgen, who pioneered MFC morphing control surfaces on our project; and Bill Otjens and Dr. William Devenport for their support at the Virginia Tech Stability Wind Tunnel. From Techsburg, Inc: Jon Fleming, Sarah Tweedie, and Matt Langford for their help fabricating the test model and executing the wind tunnel tests. From Honeywell Labs: Dale Enns and Eric Euteneuer, for their help in simulation and flight control insights. And from the Air Force Research Lab: James Davis, and Chris Perry, the Air Force program managers on my project. I would like to acknowledge and thank the Air Force Research Lab/Munitions Directorate at Eglin AFB and the Air Force Office of Sponsored Research for funding this research. iv Table of Contents ABSTRACT .................................................................................................................................... ii Acknowledgements ........................................................................................................................ iii Table of Contents ............................................................................................................................ v List of Figures ................................................................................................................................ vi List of Tables ................................................................................................................................. ix Chapter 1 Introduction and Motivation ...................................................................................... 1 1.1 Coordinate System ............................................................................................................. 3 1.2 Comparison to Other UAV Configurations ....................................................................... 5 1.3 Research Objectives ......................................................................................................... 11 1.4 Flow Control Concepts .................................................................................................... 12 Chapter 2 Literature Review and Background .......................................................................... 16 2.1 Ducted Fan Aerodynamics ............................................................................................... 16 2.1.1 Fundamental Aerodynamics ..................................................................................... 17 2.1.2 Ducted Fan Aerodynamic Modeling ......................................................................... 19 2.1.3 Ducted Fan Vehicle Design ...................................................................................... 21 2.1.4 Ducted Fan Flight Control ........................................................................................ 23 2.2 Synthetic Jets ................................................................................................................... 25 2.2.1 Synthetic Jet Fluid Mechanics .................................................................................. 26 2.2.2 Synthetic Jet Modeling ............................................................................................. 27 2.2.3 Synthetic Jet Actuator Design ..................................................................................