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Experimental Determination of Lift and Lift Distributions for Wings in Formation Flight

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Experimental Determination of Lift and Lift Distributions for Wings in Formation Flight Experimental Determination of Lift and Lift Distributions for Wings In Formation Flight Jason Gibbs A thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Engineering Mechanics Dr. Demetri Telionis, Committee Chair Dr. Pavlos Vlachos, Member Dr. Saad Ragab, Member January 25th, 2005 Blacksburg, VA Keywords: Formation flight, multi-wing formation, experimental wind tunnel tests, wings, lift, circulation distribution, wake vorticity, Trefftz plane Experimental Determination of Lift and Lift Distributions for Wings In Formation Flight Jason Gibbs (ABSTRACT) Experimental methods for the investigation of trailing vortex strengths, total lift, and lift distributions for three-dimensional wings in close proximity flight were developed. With these experiments we model compound aircraft flight either docked tip-to-tip, or flying in formation. There is a distinct lack of experimental formation flight data using three-dimensional wing models for tests. The absence of fixed walls on either end of the wing permits the development of the asymmetric shedding of vortices, and the determination of the asymmetric circulation distribution induced by the proximity of the leading wing. The pair consisted of a swept NACA-0012 non-cambered wing simulating one half of a leading aircraft and a rectangular cambered NACA 63-420 wing simulating the trailing aircraft. Important aspects of the work included theoretical development, experimental setup, data acquisition and processing, and results validation. Experimentally determining the lift for formation flight, in addition to the local flow behavior for a pair of wings, can provide valuable insight for the proposition of flying actual aircraft in formation to increase mission efficiency. To eliminate the need for bulky mounting stings and direct load measurement devices that can potentially interfere with the local flowfield, a minimally invasive velocity probe method is developed. A series of experiments were performed to assist with the development of the method. Velocity and vorticity distributions obtained along a near-field plane were processed to calculate wingtip vortex strengths. Additionally, vortex position instabilities and the shedding of vorticity inboard of the wingtips were observed. To determine the circulation distributions for the trailing wing, the initial method is modified. By processing velocity information acquired in a near-field plane, both the lift and induced drag were calculated for the trailing airfoil. Comparisons are made to directly measured loads and to results reported earlier. Directly measured lift and drag coefficients were found to agree with existing literature. ii Dedication Creation seems to come from imperfection. Creation of a significant entity when beginning with something imperfect is the ability to achieve. To every person who cannot, will not, and then does not give up nor give in when trying to accomplish what seems to be the impossible. You will prevail. ii i Acknowledgements I would like to thank my primary advisor, Dr. Demetri Telionis, first and foremost for providing me with guidance as needed throughout the duration of my studies. He has always been available whenever I was in need of assistance. I would also like to extend appreciation to Dr. Pavlos Vlachos, and Dr. Saad Ragab for serving on my graduate advisory committee. Although I didn’t often seek out their expertise, of which they both have much in their respective fields, I have no doubt that they would have welcomed my inquiries without hesitation. In addition to my technical advisors, I would like to express gratitude towards my parents. Although they may not have understood most of the research I was performing, why I had to have everything “just right”, or why it seemed to take me forever to draw this document to a close, they were accepting and supportive. Lastly, to anyone I haven’t mentioned by name here, but who has directed or assisted me along my journey through my graduate studies enabling me to get to where I am today, thank you. iv TABLE OF CONTENTS CHAPTER 1 ..................................................................................................................................1 1 BACKGROUND AND INTRODUCTION.......................................................................1 1.1 MOTIVATION ...................................................................................................................1 1.2 INTRODUCTION................................................................................................................2 1.3 TECHNICAL BACKGROUND AND METHODOLOGY...........................................................4 1.3.1 THEORETICAL AND COMPUTATIONAL RESEARCH ........................................................13 1.3.2 EXPERIMENTAL RESEARCH...........................................................................................20 1.4 OBJECTIVES...................................................................................................................22 CHAPTER 2 ................................................................................................................................24 2 EXPERIMENTAL SETUP AND PROCEDURE ..........................................................24 INTRODUCTION ..........................................................................................................................24 2.1 WING MODELS ..................................................................................................................25 2.2 WIND TUNNEL AND MODEL IMPLEMENTATION................................................................26 2.3 LOADCELL BALANCE.........................................................................................................30 2.4 FLOW MEASUREMENT PROBE ...........................................................................................31 2.5 DATA ACQUISITION SYSTEM AND POST PROCESSING ..................................................33 CHAPTER 3 ................................................................................................................................38 3 WAKE DATA METHOD .................................................................................................38 3.1 DETERMINATION OF TOTAL LIFT ......................................................................................38 3.1.1 VELOCITY INTEGRATION METHOD..................................................................................41 3.1.2 VORTICITY INTEGRATION METHOD ................................................................................44 3.2 TEST CASE FOR A SINGLE WING .......................................................................................46 3.3 APPLICATION TO FORMATION FLIGHT................................................................................50 CHAPTER 4 ................................................................................................................................55 4 METHOD DEVELOPMENT...........................................................................................55 DETERMINATION OF THE SPANWISE CIRCULATION DISTIBUTION.............................................55 CHAPTER 5 ................................................................................................................................60 5 RESULTS AND DISCUSSION ........................................................................................60 5.1 INITIAL RESULTS ................................................................................................................60 5.2 FINAL RESULTS ..................................................................................................................77 5.3 CONFIRMATION OF FLOW SEPARATION..............................................................................83 5.4 LOAD MEASUREMENTS ......................................................................................................85 v CHAPTER 6 ................................................................................................................................90 6 CONCLUSIONS AND FUTURE WORK ......................................................................90 FUTURE WORK ...........................................................................................................................98 vi TABLE OF FIGURES FIGURE 1: CLASSIFICATION OF DRAG. ............................................................................................. 4 FIGURE 2: EFFECT OF VISCOSITY ON TANGENTIAL VELOCITY COMPONENT NEAR THE VORTEX CORE: IDEAL VORTEX (LEFT) AND OSEEN VORTEX (RIGHT).................................................... 8 FIGURE 3: VELOCITY FIELDS FOR IDEAL AND OSEEN VORTICES. .................................................... 8 FIGURE 4: UPWASH / DOWNWASH REGIONS FOR A LIFTING WING. ............................................... 10 FIGURE 5: LIFTING SURFACE REPRESENTED BY A SINGLE HORSESHOE VORTEX OF CONSTANT STRENGTH Г............................................................................................................................ 11 FIGURE 6: LIFTING SURFACE REPRESENTED BY A BOUND VORTEX SHEET..................................... 12 FIGURE 7: BOUND VORTEX SHEEP SIMPLIFIED AS A SINGLE LINE FOR A LARGE ASPECT RATIO WING. ...................................................................................................................................... 12 FIGURE 8: QUADRILATERAL
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