Exploration of High-Frequency Control of Dynamic Stall Using Large-Eddy Simulations

Visbal, Miguel R.; Benton, Stuart I.

doi:10.2514/1.j056720

Cited by 61 publications

(36 citation statements)

References 69 publications

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“…The actuation signal is superimposed on the background pressure signal, modifying it slightly at St e 0.05 and significantly at St e 0.35, which is near the jet column mode Strouhal number. Similar actuator-produced perturbations (i.e., the fundamental frequency along with several harmonics) have been reported by Visbal [166,167] and Visbal and Benton [168] in a large-eddy simulation where periodic blowing and suction with a step function profile for flow separation control were employed.…”

Section: Actuatorssupporting

confidence: 64%

Excitation of Free Shear-Layer Instabilities for High-Speed Flow Control

2018

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Free shear layers are building blocks of many flows of interest in applications, including jets, cavity flows, and separated flows. It was found several decades ago that free shear layers are unstable to small perturbations over a wide range of frequencies, that they are dominated by coherent large-scale structures (even at high Reynolds numbers), and that the dynamics of these structures dominate important processes: entrainment, mixing, momentum transport, and noise generation. These findings motivated extensive research activities to actively control their development using excitation of instabilities, but early experimental research focused primarily on the control of low-speed, low-Reynolds-number free shear layers. This extensive body of the literature is briefly reviewed. The authors' recent work using localized arc filament plasma actuators in jets shows that free shear layers respond to the excitation over a large range of conditions that have been explored: jet Mach number (up to 1.65), convective Mach number (up to 1), and Reynolds number (up to 1.65 × 10 6). However, the nature of large-scale structures, shear-layer growth rate, and generation of Mach waves all depend on the jet Mach number and compressibility level. The results clearly demonstrate the similarity of instability processes and development of large-scale structures in free shear layers, regardless of the Mach or Reynolds numbers. Nomenclature

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Section: Actuatorssupporting

confidence: 64%

Excitation of Free Shear-Layer Instabilities for High-Speed Flow Control

2018

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“…LES-based investigations have also been employed, in the recent past, for concept-level exploratory studies of dynamic stall flow control using unsteady actuation near the airfoil leading edge. [25,26] The targeting of natural instabilities within the LSB was demonstrated through these studies to have a favorable impact on the airfoil aerodynamic performance, leading to a suppression of the turbulent BL separation on the airfoil surface, a significant mitigation of the overall vibratory loading, and an associated delay in the emergence of the DSV.…”

Section: Literature Reviewmentioning

confidence: 91%

Unsteady Flow Physics of Airfoil Dynamic Stall

Gupta

Ansell²

2019

AIAA Journal

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A series of wind tunnel experiments were conducted on an NACA 0012 airfoil undergoing a linear pitch ramp maneuver at a fixed dimensionless pitch rate of Ω + = 0.05 and across three transitional Reynolds numbers, Re c = 0.2 × 10 6 , Re c = 0.5 × 10 6 , and Re c = 1.0 × 10 6. The primary objectives of these experiments were to perform a detailed analysis of the flow evolution, with particular emphasis on the underlying physical mechanisms, and to extract the dominant scales associated with the flow perturbations, for a canonical dynamic stall process. A series of unsteady surface pressure measurements, with a high sampling frequency, were acquired in order to investigate the time-dependent behavior of the flow in the immediate vicinity of the airfoil. These surface pressure measurements were used to identify the region of boundary layer transition during the initial stages of the dynamic stall process. A spatially-contracting laminar separation bubble was also identified near the airfoil leading edge from the characteristic pressure plateau in the surface pressure distribution. The dominant frequencies associated with the laminar separation bubble were extracted using a continuous wavelet transform technique. These frequencies were observed to span a wide range of chordbased Strouhal numbers between St = 50 and St = 105, at Re c = 0.5 × 10 6. The off-body flow evolution was inferred and described using a combination of surface pressure measurements and time-resolved particle image velocimetry. For Re c = 0.2 × 10 6 and Re c = 0.5 × 10 6 , the dynamic stall vortex was observed to emerge from a collective interaction of the discrete vortices that were ejected from the leading edge of the airfoil. At Re c = 1.0 × 10 6 , however, the near-wall vortices were observed to amalgamate into two regions, forming a distinct primary and a secondary coherent structure. After formation, these two structures were observed to interact with each other, following a co-rotating vortex merging process and resulting in the emergence of a single, coherent dynamic stall vortex. The process of emergence of the dynamic stall vortex at Re c = 1.0 × 10 6 , observed from the present experiments, is therefore quite distinct from the classical understanding of the dynamic stall vortex formation, which was observed at the lower Reynolds numbers. The time-dependent spectra of the velocity field were calculated using a combination of empirical mode decomposition and Hilbert transformation. From the velocity spectra, the fluctuations in the flow were observed to attain an amplified state during the initial ejection of vorticity from the leading-edge region of

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“…For high Reynolds number flows, numerical simulations traditionally employ a hierarchy of turbulence models augmented in some instances with empirical transition predictions. Recently, Visbal and co-authors have employed implicit large eddy simulation (ILES) to investigate the phenomenon of dynamic stall for different flow configurations including plunging and pitching motion [12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Active flow control for drag reduction of a plunging airfoil under deep dynamic stall

Ramos

Wolf²,

Yeh

et al. 2019

Phys. Rev. Fluids

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High-fidelity simulations are performed to study active flow control techniques for alleviating deep dynamic stall of a SD7003 airfoil in plunging motion. The flow Reynolds number is Re = 60,000 and the freestream Mach number is M = 0.1. Numerical simulations are performed with a finite difference based solver that incorporates high-order compact schemes for differentiation, interpolation and filtering on a staggered grid. A mesh convergence study is conducted and results show good agreement with available data in terms of aerodynamic coefficients. Different spanwise arrangements of actuators are implemented to simulate blowing and suction at the airfoil leading edge. We observe that, for a specific frequency range of actuation, mean drag and drag fluctuations are substantially reduced while mean lift is maintained almost unaffected, especially for a 2D actuator setup. For this frequency range, 2D flow actuation disrupts the formation of the dynamic stall vortex, what leads to drag reduction due to a pressure increase along the airfoil suction side, towards the trailing edge region. At the same time, pressure is reduced on the suction side near the leading edge, increasing lift and further reducing drag.

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Exploration of High-Frequency Control of Dynamic Stall Using Large-Eddy Simulations

Cited by 61 publications

References 69 publications

Excitation of Free Shear-Layer Instabilities for High-Speed Flow Control

Excitation of Free Shear-Layer Instabilities for High-Speed Flow Control

Unsteady Flow Physics of Airfoil Dynamic Stall

Active flow control for drag reduction of a plunging airfoil under deep dynamic stall

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