The Pennsylvania State University The Graduate School Department of Aerospace Engineering AERODYNAMIC EXPERIMENTS ON A DUCTED FAN IN HOVER AND EDGEWISE FLIGHT A Thesis in Aerospace Engineering by Leighton Montgomery Myers 2009 Leighton Montgomery Myers Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science December 2009 The thesis of Leighton Montgomery Myers was reviewed and approved* by the following: Dennis K. McLaughlin Professor of Aerospace Engineering Thesis Advisor Joseph F. Horn Associate Professor of Aerospace Engineering Michael Krane Research Associate PSU Applied Research Laboratory George A. Lesieutre Professor of Aerospace Engineering Head of the Department of Aerospace Engineering *Signatures are on file in the Graduate School ii ABSTRACT Ducted fans and ducted rotors have been integrated into a wide range of aerospace vehicles, including manned and unmanned systems. Ducted fans offer many potential advantages, the most important of which is an ability to operate safely in confined spaces. There is also the potential for lower environmental noise and increased safety in shipboard operations (due to the shrouded blades). However, ducted lift fans in edgewise forward flight are extremely complicated devices and are not well understood. Future development of air vehicles that use ducted fans for lift (and some portion of forward propulsion) is currently handicapped by some fundamental aerodynamic issues. These issues influence the thrust performance, the unsteadiness leading to vehicle instabilities and control, and aerodynamically generated noise. Less than optimum performance in any of these areas can result in the vehicle using the ducted fan remaining a research idea instead of one in active service. The Penn State Department of Aerospace Engineering initiated an experimental program two years ago to study the aerodynamics of ducted lift fans. The focus of this program from its initiation was to study a single lift fan subject to an edgewise mean flow. Of particular concern was the transitional flow regime from hover to a relatively high forward speed in which a major portion of the vehicle lift is produced by the aerodynamic forces on the body. We refer to this as ducted fan edgewise flow. There are four obvious consequences of operating a ducted lift fan in edgewise (forward) flow. First, separations off the leading portion of the duct can reduce the inflow and thus the thrust of the fan. Second, the separated flow will lead to unsteadiness which will iii undoubtedly decrease the control authority of the vehicle. Thirdly, the outer surface of the fan shroud is likely to be fairly blunt. This body shape, together with the strong momentum drag of the lift fan outflow, produce excessive drag forces that increase the requirements of the propulsion devices. Finally, increased turbulence of the inflow will also result in increased production of aerodynamic noise. The goals of this project are to conduct detailed experiments on several configurations of ducted lift fans in hover and edgewise flow. Single ducted lift fan configurations involve different shrouded duct shapes and rotor shapes. Rotors are tested with a range of solidities and tip clearances. Including inlet duct vents over the forward portion of the duct shroud, has the potential of reducing the problem of separated flow over the forward portion of the duct inlet, and potentially reducing the drag of the vehicle in forward flight. iv TABLE OF CONTENTS LIST OF FIGURES .....................................................................................................x LIST OF TABLES.......................................................................................................xix NOMENCLATURE ....................................................................................................xx ACKNOWLEDGEMENTS.........................................................................................xxiii Chapter 1 Introduction ................................................................................................1 1.1 Why Ducted Fans?..........................................................................................2 1.2 Ducted Fan History.........................................................................................4 1.2.1 Fixed Wing Propulsion (Forward Flight) ...............................................4 1.2.2 Rotary Wing Propulsion (Forward Flight)..............................................5 1.2.3 Tilt Fan VTOL........................................................................................6 1.2.4 Direct Lift Fan.........................................................................................6 1.2.5 Lessons Learned from History................................................................8 1.2.6 Future and Current Outlook....................................................................9 1.3 Ducted Fan Classification...............................................................................11 1.4 Important Ducted Fan Parameters ..................................................................12 1.5 Technical Approach/Specific Goals ...............................................................15 Chapter 2 Review of Rotor Aerodynamics.................................................................18 2.1 Open Rotor in Hover ......................................................................................18 2.2 Ideal Ducted Rotor in Hover...........................................................................20 2.3 Non-Ideal Ducted Rotor in Hover ..................................................................25 2.3.1 Horn[7] Method......................................................................................25 v 2.3.2 Leishman[2] Method...............................................................................28 2.4 Hover Summary..............................................................................................32 2.5 Open Rotor in Forward Flight ........................................................................33 2.6 Non-ideal Ducted Rotor in Forward Flight ....................................................35 Chapter 3 Description of Wind Tunnel Models..........................................................40 3.1 Ford Fan Model ..............................................................................................40 3.2 LL1 Series Models..........................................................................................41 3.2.1 LL1 Rotor Selection................................................................................41 3.2.2 LL1 Motor Selection...............................................................................43 3.2.3 LL1 Duct Design.....................................................................................45 3.3 10 Series Models.............................................................................................48 3.3.1 Model 10-1 Duct.....................................................................................49 3.3.2 Model 10-2 Duct.....................................................................................51 3.3.3 10 Series Rotor Selection........................................................................54 3.3.4 10 Series Motor and Electronics Selection.............................................57 3.3.5 10 Series Motor Mount...........................................................................62 3.3.6 10 Series Isolated Rotor Model...............................................................65 Chapter 4 Induced Velocity Experiments...................................................................67 4.1 Description of Experiment..............................................................................67 4.1.1 Description of Facility............................................................................68 4.1.2 Instruments Used ....................................................................................69 4.1.3 Experiment Setup....................................................................................69 vi 4.1.4 LL1 Induced Velocity Procedures..........................................................71 4.1.5 10-1 Induced Velocity Procedures..........................................................73 4.2 LL1 Induced Velocity Experiment Results ....................................................77 4.3 Induced Velocity of Nominal 10 inch Rotors Operating Outside the Duct....82 Chapter 5 Thrust Experiments in Hover .....................................................................89 5.1 Description of Experiment..............................................................................89 5.2 Description of Facility....................................................................................90 5.2.1 APB Balance...........................................................................................90 5.2.2 Calibrating the APB Balance..................................................................93 5.2.3 Hammond Balance..................................................................................98 5.2.4 Calibrating the Hammond Balance.........................................................100 5.3 Data Acquisition Systems...............................................................................104 5.3.1 APB Data Acquisition System................................................................105 5.3.2 APB LabView Software Operation ........................................................108