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 J31: Aerodynamics: Gusts |
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Chair: Jennifer Franck, University of Wisconsin - Madison Room: 255 C |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J31.00001: Effect of Periodic Longitudinal Gusts on Airfoil Performance Under Separated-Flow Conditions and Elevated Freestream Turbulence Levels Suraj Bansal, Philippe Lavoie Canonical studies have shown that kinematic forcing in separated flow conditions can produce a leading-edge vortex, that can grow to the order of the airfoil chord length and produce significant transient loading. The present research experimentally investigates separated-flow dynamics for an airfoil under the influence of periodic longitudinal gusts. Unsteady forces over an SD7003 airfoil are measured for a wide range of gust frequencies, angles of attack, and mean Reynolds number. The results show that the mean forces increase significantly when the natural vortex shedding frequency locks in with the gust frequency. Also, the lift amplitude increases considerably when the circulatory contributions are in phase with the unsteady freestream velocity and reduces drastically when out of phase. The effects of elevated freestream turbulence levels are also considered, where turbulence intensities below 1% have a weak effect on the unsteady force generation. However, significantly different trends are observed at larger turbulence intensities. Smoke visualization and phase-averaged particle image velocimetry techniques are employed to study the associated flow physics. The final presentation will answer the following questions: 1) What is the impact of gust frequency, angle of attack and freestream turbulence levels on unsteady loads over an airfoil? 2) How are the dynamics associated with the unsteady vortical structures correlated with unsteady force generation? |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J31.00002: Numerical investigation of a vortex gust impinging on a lightweight wing Bingfei Yan, Eric Edward Handy-Cardenas, Kenneth S Breuer, Jennifer A. Franck This project computationally explores the kinematic response of a passively mounted wing impacted by a vortex gust. It is motivated by modern aircraft, which utilize flexible and lightweight materials to improve efficiency but are more susceptible to flow disturbances and gusts due to slender wings and low mass. In place of a theoretical vortex profile, the vortex is generated through an upstream airfoil with a prescribed heave and pitch profile. Numerical simulations at a Reynolds number of 1000 were conducted across a range of vortex-generation profiles. A coherent vortex is generated with a horizontal trajectory accompanied by a shear layer extending obliquely, serving to isolate the vortex gust. The vortex trajectory and strength are compared with experimental flume tests under similar configurations. The resulting motion of the downstream foil, in terms of its kinematic heave and pitch motion induced by the gust, is investigated and discussed for various vortex sizes and trajectories. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J31.00003: ABSTRACT WITHDRAWN
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Sunday, November 24, 2024 6:29PM - 6:42PM |
J31.00004: Large-eddy simulation on laminar-separation-bubble affected by swirling flow simulating propeller slipstream for low Reynolds number airfoil flow Akito Goto, Makoto Sato To investigate the effects of a propeller slipstream on a laminar separation bubble (LSB) over an airfoil, large-eddy simulations (LESs) were performed on the flow around the NACA0012 airfoil influenced by the wake of a propeller. The Reynolds number was 30,000, and the angle of attack was 7 degrees. The propeller-induced flow was simulated using an actuator disk model, and the characteristics of the swirling flow of propeller-induced flow was changed as the parameter to clarify the effects of the swirling flow of propeller slipstream on LSB characteristics. On the upwash side, as the swirl number increases, the separation point of LSB moves toward the leading edge. This is due to an increase in effective angle of attack. When the swirl number is high, there is no turbulent reattachment, and the flow bursts. On the downwash side, due to a decrease in effective angle of attack, the separation point of LSB moves linearly toward the trailing edge as the swirl number increases, and the reattachment point also moves linearly toward the trailing edge. The LSB region becomes smaller as the swirl number increases. Regarding the local lift coefficient, both the upwash and downwash sides show smaller lift coefficients as the swirl number increases. This is because the flow bursting occurs on the upwash side, while the effective angle of attack decreases on the downwash side. Additionally, in the absence of swirling flow, both the upwash and downwash sides show an increase in lift coefficient by the local increases of the uniform flow. |
Sunday, November 24, 2024 6:42PM - 6:55PM |
J31.00005: Boundary Layer Transition in High-Intensity Free-stream Turbulence at Aerodynamically Low Chord Reynolds Numbers Connor Toppings, Serhiy Yarusevych Aircraft and turbomachines that operate in the atmospheric boundary layer often experience free-stream turbulence intensities of 10% or greater. Our goal in this experimental study is to understand the effect of high-intensity turbulence on the aerodynamic loading of lifting surfaces at aerodynamically low chord Reynolds numbers where the lifting surface performance is particularly sensitive to the level of free-stream turbulence. Free-stream turbulence intensities of up to 15% and varying integral length scales were generated in a wind tunnel using an active turbulence grid. We investigate the effect of increased turbulence intensity on flow separation and laminar-to-turbulent transition on an airfoil model using particle image velocimetry and correlate it with the changes in aerodynamic loads measured using a force balance. Under conditions of elevated freestream turbulence, we find intermittent changes in the transition process that lead to notable fluctuations in the lift and drag forces, whose characteristics depend on the freestream turbulence parameters. |
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