Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X30: Aerodynamics: Wings and Flow Control |
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Chair: Ignazio Maria Viola, University of Edinburgh Room: 255 B |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X30.00001: Dynamics of triple vortex system on a supercritical wing-tip geometry Satoshi Baba, Guang C. Deng, Hadar Ben-Gida, Stéphane Moreau, Oksana Stalnov, Philippe Lavoie The system of wing-tip vortices and its dynamics on a cantilever wing with a supercritical airfoil profile under low Mach number and moderate angle of attack were analyzed. The results of Particle Image Velocimetry (PIV) in a wind tunnel reveal that in addition to the well-documented primary vortex on the tip surface and the secondary vortex on the suction surface, the strong camber of the airfoil near the trailing edge generates the additional tertiary vortex from the shear layer of the primary vortex. These tip vortices co-rotate in a helical profile, becoming similar in size and vorticity level as they are convected past the trailing edge. A computational validation was conducted with Large Eddy Simulation (LES) on the identical wing tip geometry, showing good agreement. The dynamics of these vortices were analyzed through the Proper Orthogonal Decomposition (POD) of the flow field, which indicates the presence of high-energy vortex displacement modes. The POD modes show that the displacement of the secondary vortex has low correlation with that of the primary and tertiary vortex. The unsteady surface pressure was measured to find the dominant frequency of fluctuations in each of the tip vortices, and they are shown to have a slight correlation with the angle of attack. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X30.00002: Water Tunnel Testing of Downwind Yacht Sails Ignazio Maria Viola, Jean Baptiste Souppez Downwind yacht sails, such as spinnakers, are low-aspect-ratio, highly-cambered wings with a sharp leading edge. In this talk, we will present water tunnel tests, including particle image velocimetry, of the downwind sails of a racing yacht. We will consider six model-scale rigid models at average-chord-based Reynolds numbers ranging from 5 870 to 61 870. We will discuss the critical Reynolds number above which the forces remain constant, and we will demonstrate that the sharp force increase with increasing Reynolds number is associated with the suppression of the relaminarization rather than with the laminar-to-turbulent transition. We will also discuss the upwash of the mainsail on the spinnaker and the excellent agreement between the overall performances of the sails measured in the water tunnel and those estimated by the sail designers with computational fluid dynamics. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X30.00003: The Aerodynamics of Crescent Wing Pairs in Backward and Forward Swept Orientations Mark Godfrey Mungal, Andrew K Mahler Single crescent wings of backward-swept planform shape show classical "two-time stall" lift behavior vs. angle of attack, namely an initial linear lift increase, flowed by sudden stall (first stall), followed by increasing lift (recovery) and then a loss of lift (second stall). Single forward-swept crescent wings however show a very different "rolling stall" behavior marked by a reduction of first stall, an increase of lift in the recovery region and similar lift behavior at second stall. First stall can be essentially eliminated for strongly forward-swept wings. In this study we provide results of numerical simulations using ANSYS-FLUENT on a NACA 0012 airfoil at a Re of 5.8e5 for fixed pairs of crescent wings with variable separation distances of 0.25 to 2.0 chord lengths. We find that backward-swept wing pairs show a clear interference effect where the lift coefficient is dependent upon separation distance and differs from that of a single wing. This however is not the case for forward-swept wing pairs (as seen in some tropical fish) where the lift coefficient is fairly insensitive to separation distance, and is similar to that of a single wing. In all cases the flow is complex with leading edge separations, separation bubbles, and positive and negative vorticity distributed along the span. However, in spite of this, forward-swept cescent wing pairs show robust lift behavior with an insensitivity to separation distance, while backward-swept crescent wing pairs show a clear dependence on separation distance. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X30.00004: The impact of wing planform on the unsteady dynamics during rapidly pitching plates in decelerating motion. Dibya Raj Adhikari, Matthew Mechlowitz, Anirudh Sriram, Samik Bhattacharya Natural flyers, such as birds, dynamically morph their wings to optimize wing configurations, especially during perching maneuvers that involve rapid pitch-up while decelerating to a complete stop. During this rapid pitching in decelerating motion, birds sweep their wings backward and forward. How these wing planforms aerodynamically benefit the perching maneuver remains unclear. This study investigates the functioning significance of these morphing wing platforms in the perching maneuver, focusing on the unsteady dynamics and the vortex evolution. We particularly investigate the impact of non-uniform wing curvature on the vortex dynamics and its associated unsteady aerodynamic forces (lift and drag). By analyzing the intricate interplay between wing shapes and vortex dynamics, we aim to enhance understanding of perching maneuver performance. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X30.00005: Compressibility-induced variation in drag and lift coefficients of NACA0012 airfoil Shishir Gautam, Chitrarth Prasad The goal of this investigation is to elucidate the effect of compressibility on the temporal oscillation of lift and drag coefficients of an airfoil section. To this end, we perform two-dimensional direct numerical simulations (DNS) of a NACA0012 airfoil at an angle of attack (AoA) of 5° under both compressible (Mach 0.4) and incompressible conditions. The Reynolds number (Re) based on the chord length and freestream velocity is kept constant at 5×104. Both cases exhibit periodic oscillations in lift and drag coefficients due to the vortex shedding associated with the shear layer roll-up at the leading edge of the airfoil, typical of the Re and AoA. While the incompressible case shows a nearly constant amplitude in the oscillation of the force coefficients, the compressible case exhibits intermittent excursions in the magnitude of these oscillations. The underlying physics of these transient excursions is investigated by creating an ensemble of such events and analyzing them using a recently developed conditional proper orthogonal decomposition (CPOD) framework. A deeper understanding of the underlying reasons for this amplitude variation can lead to significant improvements in aerodynamic performance of lifting surfaces. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X30.00006: Study and Control of a wall-bounded NACA 65(1)412 Airfoil at Transitional Re charles klewicki, Ari Schenkman, Geoffrey R Spedding, Gustaaf B Jacobs, Bjoern F Klose Airfoil performance within the transitional Reynolds number regime exhibits nonlinear behavior and strong sensitivity to the locations of laminar separation and turbulent reattachment. The dynamics of these phenomena are influenced by the transition of the separated shear layer. |
Tuesday, November 26, 2024 9:18AM - 9:31AM |
X30.00007: Active Flow Control Using Rotating Cylinders Samantha I Zuniga, Alejandro Carrizales, Isaac Choutapalli This research investigates the aerodynamic and flow field characteristics of a NACA 0010 airfoil equipped with rotating cylinders near the leading edge, subjected to a flow with a freestream turbulence intensity of 4.3%. The airfoil was modified to integrate five micro-DC motors positioned at 14.5% of the chord length from the leading edge. The cylinders, with dimensions of 0.75 inches in diameter and 0.5 inches in width, exposed 3mm of their length to the incoming flow. A modified leading edge with eight sinusoidal protrusions (tubercles) was employed to compare the performance of the micro-rotating cylinder airfoil with an unmodified baseline airfoil. Experimental investigations were conducted on the NACA 0010 airfoil with and without the rotating cylinders, driven by a 12-volt power supply with a counter-clockwise rotation at 3000 RPM. The experiments encompassed a Reynolds number range of 138,400 to 412,200 and variations in the angle of attack from 0 to 24 degrees. Force and torque measurements were obtained using two 6-axis force/torque transducers. The experimental findings revealed a significant increase in the maximum lift coefficient for the airfoil equipped with rotating cylinders, demonstrating a 45% enhancement compared to the unmodified baseline airfoil. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X30.00008: Mitigating transonic buffet with porous trailing edges Esther Lagemann, Steven L Brunton, Wolfgang Schröder, Christian Lagemann In today's globalized world, commercial aviation is crucial for international connectivity, offering fast air transport services for passengers and freight. However, aerodynamic instabilities like transonic buffet and the associated aeroelastic effects are still a limiting factor in the high-speed regime. Using simultaneous and synchronized Particle-Image Velocimetry and Background-Oriented Schlieren measurements, we demonstrate that porous trailing edges efficiently mitigate transonic buffet at flight conditions. These devices modify the velocity distribution in the separated boundary layer downstream of the shock wave mimicking pre-buffet flow conditions. The extended recirculation region damps instabilities associated with the shock-wave/boundary-layer interaction, while the less intense boundary layer breathing reduces pressure fluctuations in the trailing edge region with a direct impact on the shock wave oscillation. Moreover, we reveal how the particular porous material can severely affect the aerodynamic performance and that gyroid-based materials influence the aerodynamic forces favorably. Since porous trailing edges have the additional benefit of reducing acoustic aircraft emissions, they could prospectively provide faster air transport with reduced noise emissions. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X30.00009: Impact of Air Injection on the Aerodynamic Performance of a Reverse Delta Wing Operating in Ground Effect Jacob Child, Daniel Maynes Ground effect vehicles experience increased lift when flying within a chord length of a solid boundary. This experimental study investigates the impact of air injection on the aerodynamic performance of a reverse delta wing operating in ground effect. The model was tested at Reynolds numbers, Re, varying from 0 to 672,000, at angles of attack, α, ranging from 0 to 20°, and at ground-to-wing spacings of 5, 30, and 100% of the wing chord. The mass flow of the injected air ranged from 0 to 0.187 kg/s. The largest impact of injection occurred at a 5% chord height, 0.187 kg/s air injection rate, and at an angle of attack of 20°. Here lift increased by approximately 8 times compared to the no-injection condition. For this same condition, the measured drag force decreased by a factor of 1/3. Flow visualization of several test points showed air injection reduced the extent of the region of separated flow that occurred at higher angles of attack on the suction side of the wing. Air injection was not universally beneficial, for instance, at 5% chord height and α = 0°, the lift initially decreased with increased air injection, before later increasing as the air injection rate continued to increase. This "suck down" effect is documented in jet literature. The impact of increasing air injection and α were generally symbiotic in increasing lift. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X30.00010: ABSTRACT WITHDRAWN
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Tuesday, November 26, 2024 10:10AM - 10:23AM |
X30.00011: A numerical demonstration of real-time dynamic stall control Sarasija Sudharsan Dynamic stall over aerodynamic surfaces involves nonlinear variations in aerodynamic forces and moments, severe hysteresis effects, and the potential for aeroelastic instabilities and structural failure. To effectively mitigate stall, control efforts must be deployed before the formation of a characteristic dynamic stall vortex. However, stall control is challenging due to the wide range of parameters (Reynolds number, airfoil geometry and kinematics, compressibility, etc.) that influence stall onset. This study presents a numerical demonstration of stall control for unsteady airfoil kinematics using identified vorticity and pressure-based stall onset criteria. The application of these stall onset criteria, in conjunction with deep reinforcement learning (explored in recent flow control literature), could potentially extend stall mitigation capabilities across different operating conditions. |
Tuesday, November 26, 2024 10:23AM - 10:36AM |
X30.00012: Wind Tunnel Experiments of Sprayed Liquid Flaps George Loubimov, Alexander Spitzer, Michael Kinzel The Sprayed Liquid Flap (SLF) is a novel powered-lift technology that utilizes atomized liquid sprays to achieve flow control. The SLF operates under similar principles as a Jet Flap but has key differences such as 1) fluid density that is two orders of magnitude larger than the ambient air and 2) spray droplets that provide porous medium-like forces on the gas stream. This work details a recent experimental campaign aimed at confirming past numerical examinations and providing a benchmark for future efforts. The experiments were conducted in the Acoustic Wind Tunnel facility at the Naval Undersea Warfare Center Division Newport. Forces and moments were measured for two angles of attack and various velocities. Our findings confirm that the multiphase interaction between the atomized droplets and freestream flow results in increased lift and reduced drag. |
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