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Flow separation

About: Flow separation is a research topic. Over the lifetime, 16708 publications have been published within this topic receiving 386926 citations.


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Journal ArticleDOI
TL;DR: In this paper, turbulent skin friction reduction over air-and liquid-impregnated surfaces for aqueous Taylor-Couette flow is presented for the case of super-hydrophobic surfaces.
Abstract: Results on turbulent skin friction reduction over air- and liquid-impregnated surfaces are presented for aqueous Taylor-Couette flow. The surfaces are fabricated by mechanically texturing the inner cylinder and chemically modifying the features to make them either non-wetting with respect to water (air-infused, or superhydrophobic case), or wetting with respect to an oil that is immiscible with water (liquid-infused case). The drag reduction, which remains fairly constant over the Reynolds number range tested (100 ≤ Reτ ≤ 140), is approximately 10% for the superhydrophobic surface and 14% for the best liquid-infused surface. Our results suggest that liquid-infused surfaces may enable robust drag reduction in high Reynolds number turbulent flows without the shortcomings associated with conventional superhydrophobic surfaces, namely, failure under conditions of high hydrodynamic pressure and turbulent flow fluctuations.

130 citations

Journal ArticleDOI
TL;DR: In this paper, a rate equation is proposed to govern the variation of the effective turbulent viscosity, and the effects of generation, convection, diffusion, and decay are each represented by appropriate terms leaving only two empirical constants to be determined by experiment.
Abstract: A rate equation is proposed to govern the variation of the effective turbulent viscosity. The effects of generation, convection, diffusion, and decay are each represented by appropriate terms leaving only two empirical constants to be determined by experiment. This rate equation together with the equations of motion form a closed system applicable to quasiparallel turbulent shear flows. For an incompressible turbulent boundary layer with zero pressure gradient, solutions were obtained by assuming local similarity and a linear growth of the boundary‐layer thickness. Another problem, the turbulent‐nonturbulent interface at the outer edge of the boundary layer was treated by using the further assumption that the large scale motion of the interface has no significant contribution to the Reynolds stress. It can be shown that for a nearly homogeneous domain, Prandtl's mixing length theory is a limiting case of the present theory.

130 citations

Journal ArticleDOI
TL;DR: In this article, Lighthill et al. studied the influence of the Turbulent Boundary Layer on the pressure distribution over a Rigid Two-Dimensional Wavy Wall.
Abstract: of the Influence of the Turbulent Boundary Layer on the Pressure Distribution over a Rigid Two-Dimensional Wavy Wall," TN D-6477, Aug. 1971, NASA. 4 Lighthill, M. J., "On Boundary Layers and Upstream Influence II. Supersonic Flows without Separation," Proceedings of the Royal Society, Vol. A217, 1953, pp. 478 and 504; see also Quarterly Journal of Mechanics, Vol. 3, 1950, p. 303. 5 Benjamin, T. B., "Shearing Flow over a Wavy Boundary," Journal of Fluid Mechanics, Vol. 6, 1959, p. 161. 6 Miles, J. W., "On Panel Flutter in the Presence of a Boundary Layer," Journal of Aerospace Sciences, Vol. 26, No. 2, Feb. 1959, pp. 81-93. 7 McClure, J. D., "On Perturbed Boundary Layer Flows," Rept. 62-2, June 1962, M.I.T. Fluid Dynamic Research Lab., Cambridge, Mass. 8 Anderson, W. J. and Fung, Y. C, "The Effect of an Idealized Boundary Layer on the Flutter of Cylindrical Shells in Supersonic Flow," GALCIT Structural Dynamics Rept. SM62-49, Dec. 1962, Graduate Aeronautical Lab., California Institute of Technology, Pasadena, Calif. 9 Zeydel, E. F. E., "Study of the Pressure Distribution on Oscillating Panels in Low Supersonic Flow with Turbulent Boundary Layer," NASA CR-691, Feb. 1967, Georgia Institute of Technology, Atlanta, Ga. 10 Do well, E. H., "Generalized Aerodynamic Forces on a Flexible Plate Undergoing Transient Motion in a Shear Flow with an Application to Panel Flutter," AIAA Journal, Vol. 9, No. 5, May 1971, pp. 834-841. 11 Ventres, C. S., "Transient Panel Motion in a Shear Flow," AMS Rept. 1062, Aug. 1972, Princeton Univ., Princeton, N.J. 12 Garrick, I. E. and Rubinow, S. I., "Theoretical Study of Air Forces on an Oscillating or Steady Thin Wing in a Supersonic Main Stream," TN 1383, July 1947, NACA. 13 Yates, J. E., "A Study of Panel Flutter with the Exact Method of Zeydel," NASA CR-1721, Dec. 1970, Aeronautical Research Associates of Princeton, Princeton, N.J. 14 Do well, E. H. and Ventres, C. S., "Derivation of Aerodynamic Kernel Functions," AIAA Journal, Vol. 11, No. 11, Nov. 1973, pp. 1586-1588.

130 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of micro-ramp sub-boundary layer vortex generators on an incident shock wave/boundary-layer interaction at Mach 1.84 were investigated.
Abstract: Stereoscopic particle image velocimetry is used to investigate the effects of micro-ramp sub-boundary layer vortex generators, on an incident shock wave/boundary layer interaction at Mach 1.84. Single- and double-row arrangements of micro-ramps are considered. The micro-ramps have a height of 20% of the unperturbed boundary layer thickness and the measurement planes are located 0.1 and 0.6 boundary layer thicknesses from the wall. The micro-ramps generate packets of individual vortex pairs downstream of their vertices, which produce counter-rotating longitudinal streamwise vortex pairs in a time-averaged view. These structures induce a pronounced spanwise variation of the flow properties, namely the mixing across the boundary layer interface. The probability of reversed-flow occurrence is decreased by 20 and 30% for the single- and double-row configurations, respectively. Both configurations of micro-ramps stabilize the shock motion by reducing the length of its motion by about 20% in the lower measurement plane. The results are summarized by a conceptual model describing the boundary layer’s and interaction’s flow pattern under the effect of the micro-ramps.

129 citations

Journal ArticleDOI
TL;DR: In this paper, the formation and development of the vortex loop is found to be the essential feature preceding the creation of a turbulent spot which takes place near the top of a vortex loop and near the outer edge of the boundary layer.
Abstract: Water‐tank observations of the flow phenomena associated with boundary‐layer transition have revealed that a two‐dimensional discrete vortex line, which is considered to be the consequence of an amplified perturbation wave, has a strong tendency, in shear flows, to form three‐dimensional vortex loops with a marked transverse wavelength. The formation and development of the vortex loop is found to be the essential feature preceding the creation of a turbulent spot which takes place near the top of the vortex loop and near the outer edge of the boundary layer. This formation and development provides the guiding principle of laminar‐to‐turbulent transition in wakes and jets as well as in the boundary layer.

129 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023177
2022333
2021361
2020394
2019403
2018371