Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session D16: Aerodynamics: Leading Edge Vortex 
Hide Abstracts 
Chair: Melissa A. Green, Syracuse University Room: Georgia World Congress Center B303 
Sunday, November 18, 2018 2:30PM  2:43PM 
D16.00001: Vortex Dynamics on an Airfoil Pitching at High Angles Douglas Bohl, Melissa A Green The flow field around a NACA0012 airfoil undergoing large amplitude sinusoidal pitching is investigated using Particle Image Velocimetry (PIV). The airfoil is pitched symmetrically about the quarter chord point with a peak angle of ±40° at reduced frequencies of k=0.20.6 and Re_{c}=12000. Multiple experimental Fields of View (FoV) were phase averaged and combined to provide a domain 2.5c x 1.7c, with Δx= 0.004c and Δt=1/(200f). The dynamics are investigated by tracking the vortical structures induced by the airfoil motion. In all cases a strong leading edge vortex (LEV) is formed along with several weaker vortices in the boundary layer closer to the trailing edge. The LEV forms later in the cycle, and with a higher initial peak vorticity, as k increases. However, the circulation of the LEV appears to be independent of k initially once it has formed. Later in the pitching cycle, the LEV combines with the vortices that form towards the trailing edge for lower k values, increasing the circulation of the LEV. The cause appears to be the dynamics at the trailing edge and the trajectory of the leading edge vortex, both of which are dictated by the reduced frequency of the airfoil pitching motion. 
Sunday, November 18, 2018 2:43PM  2:56PM 
D16.00002: FTLE analysis of unsteady flow around pitching airfoils of high amplitude Youwei Liu, Doug Bohl, Melissa A Green The finitetime Lyapunov exponent (FTLE) method was used to analyze the unsteady flow around NACA 0012 airfoil pitching at high amplitude (±40°), with reduced frequencies of k = 0.2 − 0.6 and Rec = 12000. Phaseaveraged particle image velocimetry (PIV) was used to obtain 14 windows of the twocomponent velocity field, that were then mirrored to represent the opposite half of the period, as the airfoil motion was symmetric. The fields of view were stitched together in postprocessing to obtain a window that was approximately 2.37 c by 1.65 c. Due to the temporal and spatial resolution of the data set, both a primary and secondary LEV were resolved in the FTLE results. The vortex tracking via FTLE was compared with Eulerian tracking methods, and then with the calculation of LEV circulation. The interactions of the distinct vortices near the airfoil surface were also investigated using FTLE, to determine the behavior of the Lagrangian attracting and repelling ridges as vortices shed and/or merge. 
Sunday, November 18, 2018 2:56PM  3:09PM 
D16.00003: Numeric Study of Dynamic Stall on an Airfoil Undergoing Constant Pitch Rate Motion Harry Werner IV, Douglas Bohl, Brian Helenbrook Dynamic stall is a flow separation phenomenon that occurs for airfoils experiencing dynamic changes in the Angle of Attack (AoA) past the static stall angle. The current study utilizes a spectral element simulation code, Nek5000, to study dynamic stall on a NACA0012 airfoil with a constant pitch rate then hold motion profile. The airfoil is pitched from 0° to 50° with a nondimensional pitch rate of Ω*=0.1. When the motion is completed the airfoil is held fixed at 50° and the simulation is allowed to continue. The computational mesh has been developed to allow for study of both the initial formation of the dynamic stall vortex near the leading edge and the interaction/evolution of this vortex as the simulation proceeds. The goal of this study is to investigate passive control strategies on the leading edge of the airfoil to mitigate the effects of dynamic stall. 
Sunday, November 18, 2018 3:09PM  3:22PM 
D16.00004: Jet Switching Precedes Chaos in the Wake of a Simultaneously PitchingPlunging Airfoil Chandan Bose, Sayan Gupta, Sunetra Sarkar This study investigates the transitional flow dynamics in the wake of a pitchingplunging airfoil in the low Reynolds number regime. In the periodic regime, the transition from Karman to reverse Karman vortexstreets and the subsequent wake deflection with a gradual increase in the amplitude based Strouhal number (St) are well investigated in the literature. However, a further increase in St may result in chaotic transition of the wake which has largely remained unexplored. The present study aims to understand the role of the main flowfield structures in triggering chaos in the wake and resolve the underlying flow physics. It is observed that the deflected trailing jet undergoes switching of direction in the farfield prior to the chaotic regime. The switching location in the downstream approaches the trailingedge and the switching frequency increases as St is increased. Eventually, the wake becomes chaotic through a series of rapid aperiodic modeswitching of the jet. Leadingedge vortex is also seen to play an important part in triggering the jet switching phenomenon. The behavior of the unsteady flowfield during these dynamical changes is studied in terms of underlying vortex interactions in the near and farfields. 
(Author Not Attending)

D16.00005: Effects of inertiainduced surface deformation on the transient lift force of oscillating airfoils Firas Siala, James A. Liburdy The effect of surface deformation on the lift force production of a sinusoidally heaving and pitching airfoil is experimentally investigated for reduced frequencies of k = fc/U = 0.10 – 0.18, pitching amplitude of θ = 70° and heaving amplitude of h_{0}/c = 0.6. The finitedomain impulse theory is used to estimate the transient lift force from the velocity fields measured using particle image velocimetry. To achieve surface deformation, the leading or the trailing onethird of the airfoil was attached to the main body using a hinging mechanism based on a torsion rod. The results show that airfoil deformation at the trailing edge increases the lift force production relative to the rigid airfoil, by enhancing the strength and advection velocity of the leading edge vortex. In addition, it is shown that at low reduced frequencies, the deforming trailing edge can suppress the formation of the trailing edge vortex, thereby decreasing its liftdiminishing effects. Furthermore, surface deformation at the leading edge is shown to negatively influence the lift force when compared to the rigid airfoil, by causing a premature leading edge vortex detachment from the airfoil surface. 
Sunday, November 18, 2018 3:35PM  3:48PM 
D16.00006: A Simple Analytical Vortex Loop Model for the Unsteady Lift of Rotating Wings Juhi Chowdhury, Matthew Ringuette Mathematical modeling of unsteady aerodynamics, including flapping wings, has gained popularity because of its application to micro air vehicle design and flight control. However, most of the existing models are not purely analytical, very expensive to implement, or twodimensional. We develop a simple 3D theoretical model for the lift force on a rotating wing starting from rest using vortex loop dynamics. Experiments and simulations have shown that the rotating wing flow exhibits a largescale loop structure around the wing, consisting of the leadingedge vortex, tip vortex, root vortex, and starting vortex. The fluid inertial force is derived using potential flow theory. The loop circulation is found from an impulse balance, and through algebraic manipulation, the circulatory lift force is established. This model is compared with six different experimental cases with various aspect ratios and starting motions, and produces a satisfactory match. Further, the formation time of the vortex loops is determined from the timevarying circulation, and compared with the universal formation time. 
Sunday, November 18, 2018 3:48PM  4:01PM 
D16.00007: Three dimensional visualization of leading edge vortex structure of a pitching and rolling wing in forward flight Brian S Thurow, Kyle Johnson, Kevin J Wabick, Randall L Berdon, James H. Buchholz Plenoptic particle image velocimetry is used to visualize the three dimensional vortex topology of an aspectratio 2.0 flatplate wing undergoing independent and simultaneous pitching and rolling motions in the presence of a free stream with Reynolds number of 10,000. The dimensionless pitch rate, k, and advance ratio, J, was varied from 0.2 to 0.5 and 0.5 to 1.25, respectively. Threedimensional, threecomponent velocity fields acquired at different phases of the motion depict a leading edge vortex (LEV) structure that initially grows and then sheds as the pitch angle increases with threedimensional details of the LEV topology highly dependent on the parameters given above. In the simultaneous pitch and roll case, features of both pure roll and pure pitch vortex topologies are present with their relative strength dependent on a parameter, π_{rot}, that combines the competing influences of k and J. 
Sunday, November 18, 2018 4:01PM  4:14PM 
D16.00008: Passive Bleeding Applied to a Wing in a Roll Maneuver Randall L Berdon, Kevin J Wabick, James H. Buchholz, Kyle Johnson, Brian S Thurow The leadingedge vortex (LEV) is an inherent feature of high angleofattack aerodynamics, impacting the forces acting on the wing. The early development of an LEV produced by a rolling wing can be classified as conical or nonconical (often manifested as an approximately symmetric archshaped structure shed from the wing). The classification depends on a nondimensional velocity gradient or centripetal acceleration parameter, π_{rot}, which accounts for the effects of both advance ratio and radius of gyration. Dye visualization of the LEV produced by a rolling rectangular plate wing of aspect ratio two was performed for a nondimensional radius of gyration of 3.25 and advance ratio, J=0.54 (π_{rot} =0.238), which has been shown to produce a conical vortex structure. Passive bleed was applied by a hole through the wing near the root and leading edge. Visualizations revealed that a significant change occurred that altered the flow from a conical to nonconical behavior. Transport analysis using PIV measurements were performed to understand physical mechanisms governing this fundamental change in flow evolution. 
Sunday, November 18, 2018 4:14PM  4:27PM 
D16.00009: Transport Mechanisms Governing initial LeadingEdge Vortex Development on a Rolling Wing Kevin Wabick, Randall L Berdon, James H. Buchholz, Kyle Johnson, Brian S Thurow

Sunday, November 18, 2018 4:27PM  4:40PM 
D16.00010: Genetic algorithm based optimisation of wing rotation in hover Alexander Gehrke, Guillaume De GuyonCrozier, Karen Mulleners The pitching kinematics of an experimental hovering flapping wing setup are optimised by means of a genetic algorithm. The pitching kinematics are parameterised with 7 degrees of freedom to allow for complex nonlinear and nonharmonic pitching motions. Two optimisation objectives are considered: maximum stroke average efficiency and maximum stroke average lift. Solutions for both scenarios converge within less than 30 generations. The most efficient pitching motion is smoother and closer to a sinusoidal pitching motion, whereas the highest lift generating motion has sharper edges and is closer to a trapezoidal motion. In both solutions the rotation is advanced with respect to the sinusoidal stroke motion. The most efficient pitching motion is characterised by a nearly constant and relatively low effective angle of attack at the start of the half stroke. This supports the formation of a leading edge vortex close to the airfoil surface that remains bound for most of the half stroke. The highest lift generating motion has a larger effective angle of attack. This leads to the generation of a stronger leading edge vortex and higher lift coefficient than in the efficiency optimised case. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2023 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700