The Effect of Slot Configuration on Active Flow Control Performance of Swept Wings at Low Reynolds Numbers Thesis Presented in Partial Fulfillment of the Requirements for Graduation with Honors Research Distinction in Aeronautical and Astronautical Engineering at The Ohio State University By Ali N. Hussain B.S. Program in Aeronautical and Astronautical Engineering The Ohio State University Department of Mechanical & Aerospace Engineering April 2018 Thesis Committee Dr. Jeffrey P. Bons, Advisor Dr. Clifford Whitfield, Committee Member © Copyright by Ali N. Hussain 2018 2 Abstract Active flow control (AFC) in the form of a discrete wall normal slot was investigated on a NACA 643-618 laminar wing model. The wing model has a leading-edge sweep of (Λ = 30°) and tests were performed using a chordwise Reynolds number of 100,000 with specific focus on the stall characteristics and performance of AFC while reducing energy needs. The study included comparing a segmented slot to a single continuous slot as well as the positioning of the slot itself along the chord at a spanwise location of z/b = 70%. For an Aeff/A of 0.5 (as compared to the original slot) maximum lift performance improved 9.6% for multiple slots while a single slot improved the maximum lift by 8.3% over the baseline. Surface flow visualization using tufts revealed that a single slot is much more effective at stopping spanwise flow and delaying stall to a higher angle of attack by 4°. For an Aeff/A of 0.75 (as compared to the original slot), lift performance improved 15.6% and 16.2% by covering x/c = 25% of the slot on the pressure and suction side of the airfoil, respectively. Covering the pressure side of the slot yielded lower drag from 20° - 24°. Through all configurations, the maximum lift coefficient is seen to depend on and increases with added Cμ. However, other performance characteristics such as drag and stall angle depend on the physical configuration of the slot. In addition, the configuration of the slot can also impact the pitching stability of the wing and delay the onset of an unstable pitching moment by up to 20°. Future work may seek to target ii specific performance areas by strategically placing the slot or only activating certain portions of the slot. iii Acknowledgments I would like to acknowledge the many people that helped me through this journey and have had an impact on my time here at The Ohio State University. Firstly, I would like to thank my advisor, Dr. Bons, for his guidance and encouragement throughout my project and for the opportunity to perform undergraduate research. This has been an incredible experience and will certainly shape my future education and career and help me to grow as an engineer and an individual. I would also like to thank Michael Walker for teaching me the ins and outs of research and answering the many questions I had, no matter how simple or complex they were. You helped me to better understand the research process and how to critically think about the problems at hand. Next, I would like to thank my fellow students in the lab for all of their help this year be it by bouncing ideas or assisting with equipment for my project. I would also like to thank Josh Geuth from the machine shop for always offering a helping hand when I needed one. I would like to thank the College of Engineering Honors Program for their financial support of this project. Lastly, and most importantly, I would like to thank my parents, Nafisa and Nayyer Hussain, as well as my brother, Mustafa Hussain. They passed on a passion for learning that has helped me succeed in the past and keeps me motivated for the future iv challenges ahead. They have always supported me through my endeavors and this thesis was possible because of their support and encouragement. v Vita 2014…………………………………………………………………..Ontario High School 2018…….…B.S. Aeronautical and Astronautical Engineering, The Ohio State University Fields of Study Major Field: Aeronautical and Astronautical Engineering vi Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. iv Vita ..................................................................................................................................... vi List of Tables ................................................................................................................... viii List of Figures .................................................................................................................... ix Nomenclature ...................................................................................................................... x Chapter 1. Introduction ....................................................................................................... 1 Chapter 2. Experimental Setup .......................................................................................... 6 2.1 Wind Tunnel ............................................................................................................. 6 2.2 Airfoil ........................................................................................................................ 7 2.3 Active Flow Control via Discrete Slots .................................................................... 9 2.4 Data Acquisition ..................................................................................................... 13 2.4.1 Global Wing Forces ......................................................................................... 13 2.4.2 Surface Flow Visualization .............................................................................. 15 Chapter 3: Results ............................................................................................................. 17 3.1 Baseline Configuration ........................................................................................... 17 3.2 Overall Global Force Results .................................................................................. 20 3.3 Global Forces: Discrete Slot Configurations .......................................................... 24 3.3.1 Aeff/A = 0.5; Configuration #1 & #3 ................................................................ 24 3.2.2 Aeff/A = 0.75; Configuration #2 & #4 .............................................................. 27 3.4 Surface Flow Visualization: Fluorescent Tufts....................................................... 33 3.5 Comparison of present study to Walker, et. al. [10] ................................................. 37 Chapter 4: Conclusion....................................................................................................... 44 References ......................................................................................................................... 47 vii List of Tables Table 1: Testing Configurations ....................................................................................... 10 Table 2: Drag Characteristics of AFC Configurations ..................................................... 23 viii List of Figures Figure 1: Low Speed Wind Tunnel (LSWT) at the Aerospace Research Center ............... 7 Figure 2: NACA 643-618 airfoil profile.............................................................................. 8 Figure 3: AFC wing mounting configuration ..................................................................... 9 [10] Figure 4: AFC slot geometry ........................................................................................ 10 Figure 5: Diagram of flow control system ........................................................................ 12 Figure 6: Taped configuration #1 ..................................................................................... 13 Figure 7: Load Cell Shaft mounting ................................................................................. 14 Figure 8: Effect of tape on baseline slotted wing; CL vs. α (left), ΔCL vs. α (right) ......... 18 Figure 9: CP distribution for AFC BR=4 directly outboard of slot, taken from CFD [12] simulation from Walker ................................................................................................ 19 Figure 10: CL vs. α performance of all AFC configurations, BR=4 ................................. 21 Figure 11: CM vs. α performance of all ACF configurations, BR=4 ................................ 22 Figure 12: CD vs. α performance of all ACF configurations, BR=4 ................................. 23 Figure 13: CL vs. α Performance of AFC configurations #1 & #3, BR=4 ........................ 25 Figure 14: CM vs. α Performance of AFC configurations #1 & #3, BR=4 ....................... 26 Figure 15: (a) Taped Configuration #2 (x/c = 25%, pressure side covered) and (b) Taped Configuration #4 (x/c = 25%, suction side covered) ........................................................ 28 Figure 16: CL vs. α Performance of AFC configurations #2 & #4, BR=4 ........................ 29 Figure 17: Schematic of Configurations #2 & #4 air blowing.......................................... 30 Figure 18: CL vs. α forces caused by AFC configurations #2 & #4, BR =4 ..................... 31 Figure 19: CM vs. α Performance of AFC configurations #2 & #4, BR=4 ....................... 32 Figure 20: Baseline wing at 훼 = 0° (left), 18° (middle), 28° (right) ..............................