Topic
Airfoil
About: Airfoil is a research topic. Over the lifetime, 24696 publications have been published within this topic receiving 337709 citations. The topic is also known as: aerofoil & wing section.
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TL;DR: In this article, the thrust and propulsive efficiency of a NACA 0012 airfoil undergoing oscillating pitching motion at a Reynolds number of 2 was investigated using a pair of force transducers to measure fluid forces directly.
Abstract: We experimentally investigate the thrust and propulsive efficiency of a NACA 0012 airfoil undergoing oscillating pitching motion at a Reynolds number of . While previous studies have computed thrust and power indirectly through measurements of momentum deficit in the object’s wake, we use a pair of force transducers to measure fluid forces directly. Our results help solidify a variety of experimental, theoretical and computational answers to this classical problem. We examine trends in propulsive performance with flapping frequency, amplitude and Reynolds number. We also examine the measured unsteady forces on the airfoil and compare them with linear theory dating from the first half of the 20th century. While linear theory significantly overpredicts the mean thrust on the foil, its prediction for the amplitude and phase of the time-varying component is surprisingly accurate. We conclude with evidence that the thrust force produced by the pitching airfoil is largely insensitive to most wake vortex arrangements.
98 citations
TL;DR: In this article, the role of acoustic feedback instabilities in the tonal airfoil self-noise phenomenon is investigated, and a linear stability analysis of the time-averaged boundary layer profiles is performed.
97 citations
TL;DR: The coarse-grid accuracy for the original CUSP scheme is improved by modifying the limiter function used with the scheme, giving comparable accuracy to that obtained with the MATD scheme, which is analyzed and compared in detail with scalar dissipation and matrix dissipation schemes.
97 citations
TL;DR: In this paper, the authors examined two cases of unsteady flowfields over a NACA 0012 airfoil at an angle of attack, and showed that the classical unstaidy Kutta condition is clearly not valid.
Abstract: Two cases of unsteady flowfields over a NACA 0012 airfoil at an angle of attack are examined. The first is the classical pitching motion about the airfoil's quarter chord. The second is the flow over a fixed airfoil immersed in the wake of the pitching airfoil. Large reduced frequencies are examined. Measurements were obtained in a water tunnel by laser Doppler velocimetry. Ensemble-averaged velocity measurements were obtained in the vicinity of the trailing edges of both the pitching and the fixed airfoil. The results indicate that the classical unsteady Kutta condition is clearly not valid. An extension of this condition earlier proposed by Giesing and Maskell is examined and some evidence is provided for its support.
97 citations
TL;DR: In this paper, it was shown that the transonic potential flow partial differential equation admits nonsymmetric solutions with large positive or negative lift, for symmetric airfoils at zero angle of attack.
Abstract: The two-dimensional transonic potential flow equation, when solved in discrete form for steady flow over an airfoil, has been found to yield more than one solution in certain bands of angle of attack and Mach number. The most striking ex- ample of this is the appearance of nonsymmetric solutions with large positive or negative lift, for symmetric airfoils at zero angle of attack. The behavior of these "anomalous" solutions is exam- ined as grid size is varied by large factors and found to be not qualitatively different from that of %ormalrf solutions (outside the nonuniqueness band). Thus it appears that the effect is not due to discretization error, and that the basic tran- sonic potential flow partial differential equation admits nonunique solutions for certain values of angle of attack and Mach number.
97 citations