Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session U03: Aerodynamics: Fixed Wings |
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Chair: Vrishank Raghav, Auburn University Room: 130 |
Tuesday, November 22, 2022 8:00AM - 8:13AM |
U03.00001: Examining the Effects of Turbulence on Low-Speed Airfoil Lift Performance Myles Mackie, Colin Stutz, John T Hrynuk Understanding how turbulence affects lift performance at low Reynolds numbers is important to predicting airfoil behavior in common flight conditions. Flow fields and force data were measured for full-span NACA 0012, Eppler 387, and SD 5060 airfoils at a Reynolds number of 12,000. Data was collected at static angles of attack from -5 to 20 degrees with freestream turbulence intensities of 0.5%, 2.5%, and 7%. Force data was also collected at Reynolds numbers of 30,000 and 60,000 with freestream turbulence intensities of 0.5% and 7%. This allowed for a broader investigation on the effects of turbulence across the low-Reynolds number regime for both symmetric and cambered airfoils. The tested airfoils were designed for laminar flow conditions, but the results of this work suggest that freestream turbulence makes the lift performance of these airfoils more linear, similar to their performance at higher Reynolds numbers. |
Tuesday, November 22, 2022 8:13AM - 8:26AM |
U03.00002: Effect of ground on a perching maneuver. Dibya Raj Adhikari, Samik Bhattacharya An experimental investigation is carried out to understand the effect of ground proximity on a perching maneuver. Different pitch rates are executed during the decelerating motion at different ground heights to test the influence of ground proximity on the aerodynamic performance of a perching wing. We also extended this study by introducing the time delay between decelerating and pitching motion to analyze its effect on the generation of unsteady forces. Here, the unsteady forces were measured by using the force sensor, and the evolution of the unsteady flow around the perching wings was captured by using a two-dimensional particle image velocimetry (PIV). This study shows that for the given pitch rate the unsteady lift force increase with the increase of ground proximity. This indicates that the perching birds can generate the same amount of lift force at slower pitch rates when the perching motion is carried out close to the ground, which explains the reason why natural flayers like birds, i.e., eagle, glide close to the ground while executing the perching maneuver during landing flight. |
Tuesday, November 22, 2022 8:26AM - 8:39AM |
U03.00003: Dynamics and Transport within Delta Wing Leading-Edge Vortices Mohammad Elsouht, James H Buchholz Three-dimensional Particle-Tracking Velocimetry measurements were obtained on a non-slender delta wing with leading-edge sweep angle of 50 degrees and sharp leading edges in order to examine the dynamics and transport processes within the leading-edge vortices. Experiments were conducted in a wind-tunnel at Reynolds numbers on the order of 10^5, and analyzed through the scope of a vorticity transport framework. Data-driven analysis techniques are also employed to subsets of the flow to examine the dynamics of dominant structures in the flow and gain further insights into the transport mechanisms. |
Tuesday, November 22, 2022 8:39AM - 8:52AM |
U03.00004: Unsteady Loading of a Wing in Convective Streamwise Gusts John A Farnsworth, Dasha Gloutak, Kenneth E Jansen The aerodynamic response of wings in unsteady streamwise gusts has been primarily researched in closed test section environments, which impose a spatially uniform yet time-varying change in velocity. However, these conditions do not necessarily represent free flight conditions where the gust velocity may vary spatially. In this study, the aerodynamic performance is examined for a wing in a convective gust generated in an open test section environment, which imposes both temporal and spatial velocity gradients. Unsteady surface pressure, forces, and moments were measured for a NACA 0015 wing and analyzed with respect to the spatial velocity distribution imposed by the convective gusts. The surface pressure scales with the local velocity, thereby altering the unsteady forces and moments experienced by the wing. The appropriate choice in reference velocity, when the surrounding environment is composed of large spatial variations, was found to be critical in characterizing the wing's unsteady response. |
Tuesday, November 22, 2022 8:52AM - 9:05AM |
U03.00005: Unsteady Loading of a Wing in Global Streamwise Gusts Dasha Gloutak, Kenneth E Jansen, John A Farnsworth Characterizing the aerodynamic response of wings to oncoming gusts is critical to maintaining stability and efficiency of aircraft. In this study, surface pressure and particle image velocimetry measurements are used to analyze the unsteady flow physics of a separated NACA 0015 wing in global streamwise gusts, which impose a time-varying velocity on the wing. Unsteadiness exhibited in the wing's aerodynamic response to velocity acceleration and deceleration can be attributed to the dynamics of developing vortical structures on the suction side. Whether the flow is accelerating or decelerating determines the temporal and spatial scales of the vortical structures, including the convective time, size, and location from which vortical structures develop and shed. These scales determine the degree to which vortical structures interact with each other and with the wing surface, thereby also influencing the unsteady loading on the wing. |
Tuesday, November 22, 2022 9:05AM - 9:18AM |
U03.00006: Computational Comparisons to Experimental Streamwise Gust Interactions Preston Tee, Dasha Gloutak, John A Farnsworth, Kenneth E Jansen Unsteady aerodynamics can have a significant effect on small scale aircraft, motivating the study of how convectively evolving gusts interact with wings at low Reynolds numbers. Computational study of this problem allows for access to the flow physics from the entire, spatially and temporally evolving flow field, but requires careful setup of the simulation conditions to accurately capture the flow phenomena characteristic of low Reynolds number boundary layers. Therefore, a single interesting configuration identified from the unsteady experiment was studied carefully to first understand the computational behavior and accuracy of the flow in steady conditions within the range of Reynolds numbers of the unsteady case. Results of LES simulations performed within this range of Reynolds numbers are directly compared to their experimental counterparts in order to assess the simulation's ability to accurately match the experiment under the same conditions. |
Tuesday, November 22, 2022 9:18AM - 9:31AM |
U03.00007: The analytical and experimental study of the controlled spanwise-twisting maneuver. Kamlesh Joshi, Samik Bhattacharya We have experimentally and analytically investigated the effect of controlled spanwise twisting maneuver at Re 10000. We have performed the experiment for two Angle of attack. First AOA is 5 degree which is below the static stall angle and AOA=15 degree which is above the static stall angle. The results have shown an increase in lift and drag coefficient value as the twisting starts. The initial rise in the lift forces happens due to inertial forces. At angle of attack 5o, there is no dip in the lift coefficient after the twisting whereas in case of AOA 15o there is a delayed dip in the lift coefficient. The results of spanwise PIV experiments at 90%, 85% and 60% have shown the difference in Leading-Edge Vortex (LEV) development for straight and the twisting case. For the twisting case at 85 percent plane, we saw more separation in the flow near the leading edge. At the 60 percent span we have not seen a significant difference in vortex formation. We have developed an analytical model which is derived from Wagner’s theory and Lifting line theory. This model was able to predict lift with good accuracy for the small angle of attacks. For the larger angle of attacks (greater than 5o), the discrepancies in the force value increases. Another model which we have developed can be implemented for higher AOA. In that model we have used leading edge suction parameter to LESP to model the leading edge vortex which forms when the value of the absolute LESP is higher than critical LESP. |
Tuesday, November 22, 2022 9:31AM - 9:44AM |
U03.00008: On the interplay between flow and pressure fields around an airfoil undergoing dynamic stall Jibu T Jose, Yuhui Lu, Karuna Agarwal, Joseph Katz The evolution of pressure distribution around a 50mm chord, NACA 0015 airfoil, harmonically pitched between 5o to 25o, hence undergoing dynamic stall, was studied at reduced frequency (k) varying between 0.047 to 1.57 and Reynolds number (Re) between 13,600 to 136,000. Time resolved stereo-PIV measurements in the JHU refractive index matched water tunnel facilitated simultaneous measurements on both sides of the airfoil. The pressure field was computed by spatial integration of the material acceleration, assuming a 2D flow, using a GPU-based, parallel line, omni directional method. The lift and moments were calculated by integration of the pressure along the surface. The pressure induced as the dynamic stall vortex (DSV) migrated along the suction side was a prominent contributor to the delay in stall onset, and reduced frequency-dependent location of pressure minimum and angle of maximum lift. Fragmentation of the DSV near the trailing edge (TE) caused a sudden drop in lift. Entrainment of the pressure side vorticity by the DSV created a low-pressure region near the TE, and a short-lived peak in the leading-edge moment. A DSV location-based time scale, determined from the surface pressure gradients, was used to collapse the lift curves for different Re and k. |
Tuesday, November 22, 2022 9:44AM - 9:57AM |
U03.00009: Laminar separation bubble bursting and formation on a finite wing in an unsteady freestream. Connor Toppings, Serhiy Yarusevych The transient dynamics of laminar separation bubble formation and bursting on a cantilevered NACA 0018 finite wing model with an aspect ratio of 2.5 and an angle of attack of 6° is studied experimentally in a wind tunnel. Bubble bursting and formation are induced by a change in the freestream velocity that changes the chord Reynolds number between limiting values producing either a long or short bubble under steady state conditions. Time-resolved direct force measurements are employed to characterise the transient response of global lift and drag forces to bubble bursting and formation. Simultaneous with force data acquisition, stereo particle image velocimetry is performed in a series of planes on the suction surface of the wing to link the unsteady loading to the transient development of the separation bubble and quantify the influence of unsteady wing tip and wing root effects on the bursting and formation processes. The results provide novel insight into the dynamics of bubble bursting and formation on a finite wing and the associated changes in aerodynamic loading. |
Tuesday, November 22, 2022 9:57AM - 10:10AM |
U03.00010: Aeroelastic instabilities and three-dimensional vortex dynamics of pitching swept wings Yuanhang Zhu, Kenneth Breuer We experimentally study the aeroelastic instabilities and three-dimensional vortex dynamics of pitching swept wings, with the sweep angle ranging from 0 to 25 degrees. We show that the aeroelastic instability boundary changes non-monotonically with the sweep angle, due to the non-monotonic power transfer between the ambient fluid and the elastic mount. An optimal sweep angle (10 degrees) is observed to promote flow-induced oscillations. Force and moment measurements show that the power transfer of the aeroelastic system is governed by the magnitude and phase of the unsteady aerodynamic moment. The wing sweep is found to have no effect on the unsteady lift and drag, indicating that it regulates the aerodynamic moment by changing the moment arm. Three-dimensional flow structures measured by multi-layer stereoscopic particle image velocimetry are analyzed to explain the differences in the moment generation for different swept wings. Finally, we employ a physics-based force and moment partitioning method to quantitatively correlate the three-dimensional leading-edge and tip vortex dynamics with the resultant unsteady aerodynamic moment, which further governs the power transfer and thus the stability of the aeroelastic system. |
Tuesday, November 22, 2022 10:10AM - 10:23AM |
U03.00011: Post stall aerodynamic response of a wing in a tandem arrangement – effect of spacing and aspect ratio of downstream wing Syed Hassan Raza Shah, Anwar Ahmed, Luqman Ahmed The effect of streamwise spacing and aspect ratio of the downstream wing on the post-stall aerodynamic response of the upstream wing was experimentally investigated at a chord-based Reynolds number of 100,000. Wings consisting of a NACA0012 profile having a chord length of 4 inches were utilized. The aspect ratio of the rear wing varied from 0.5 to 5. The streamwise spacing between the trailing edge of the front wing and the leading edge of the rear wing varied from 0.5c to 4.5c. The angle of attack α of the upstream wing was changed statically between 0o to 80o while the downstream wing remained at α = 0o. It was found that the presence of the downstream wing did not change the pre-stall lift curve slope, maximum lift coefficient and stall angle of the upstream wing, but the post-stall behaviour was significantly altered. The increase in lift due to the increase in the angle of attack beyond stall-angle was much less than an isolated wing when the spacing between the wings was minimum. For streamwise spacing >1.0c, the post-stall lift curve slope values followed an isolated wing curve up to a critical angle of attack, after which a sudden secondary stall was observed. Unlike a conventional stall, where the decrease in the lift is accompanied by an increase in drag, the secondary stall caused a significant reduction in both lift and drag. The critical angle of attack increased with the increasing streamwise spacing but only when the projected wing area in the flow direction was approximately equal to or greater than 25% of the spacing between the wings. The secondary stall remained insensitive to the changes in the aspect ratio of the downstream wing. Flow visualization indicated that the rear wing suppressed the wake of the upstream wing in the post-stall angles of attack range, and the vortices originating from the trailing edge and shear layer from the leading edge of the front wing did not cross the wake centerline. |
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