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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, the authors describe the behavior of a turbulent boundary layer on a smooth, axisymmetric body exposed to an adverse pressure gradient of sufficient strength to cause a short region of mean reverse flow ('separation'), which is tailored such that the boundary layer reattaches and then develops in a nominally zero pressure gradient.
Abstract: This paper describes the behaviour of a turbulent boundary layer on a smooth, axisymmetric body exposed to an adverse pressure gradient of sufficient strength to cause a short region of mean reverse flow ('separation’). The pressure distribution is tailored such that the boundary layer reattaches and then develops in a nominally zero pressure gradient. Hot-wire and pulsed-wire measurements are presented over the separated region and downstream of reattachment. The response of the turbulence quantities to separation and to reattachment is discussed, with emphasis on the relaxation behaviour after reattachment. Over the separation bubble, the response is characteristic of that seen by other workers: the Reynolds stresses in the inner region are reduced and stress peaks develop away from the wall. At reattachment, the skewness of the fluctuating wall shear stress vanishes, as it is known to do at separation. After reattachment, the outer-layer stresses decay towards levels typical of unperturbed boundary layers. But the inner-layer relaxation is unusual. As the viscous wall stress increases downstream of reattachment, the recovery does not start at the wall and travel outward via the formation of an ‘internal’ layer, the process observed in many other relaxing flows. In fact, the inner layer responds markedly more slowly than the outer layer, even though response times are shortest near the wall. It is concluded that the large-scale, outer structures in the turbulent boundary layer survive the separation process and interfere with the regeneration of Reynolds stresses in the inner region after reattachment. This behaviour continues for at least six bubble lengths (20 boundary-layer thicknesses) after reattachment and is believed to have profound implications for our understanding of the interaction between inner and outer layers in turbulent boundary layers.

92 citations

Journal ArticleDOI
TL;DR: Preliminary studies with pulsatile flow and with blood demonstrate that boundary layer separation occurs under clinical flow conditions, and may play a role in the development of anastomotic hyperplasia and atherosclerotic deposits in the vicinity of surgicalAnastomoses.
Abstract: • We performed an investigation of boundary layer separation in models of side-to-end anastomoses, used clinically in axillofemoral and femorofemoral grafting. Boundary layer separation occurs when momentum causes a fluid to flow against a local pressure gradient. Models of side-to-end anastomoses were constructed from Dacron grafting material and from clear plastic blocks and tubing. Fluid energy loss across the anastomosis was small and physiologically insignificant. Local adverse pressure gradients were demonstrated near the anastomosis. Flow visualization studies demonstrated characteristic areas of boundary layer separation in the region of the adverse pressure gradients. The separation region involved both the main limb and the side arm. The separation forms a shell or ring of slow-moving fluid around the mainstream. Preliminary studies with pulsatile flow and with blood demonstrate that boundary layer separation occurs under clinical flow conditions. Boundary layer separation may play a role in the development of anastomotic hyperplasia and atherosclerotic deposits in the vicinity of surgical anastomoses. (Arch Surg114:1369-1373, 1979)

91 citations

Journal ArticleDOI
TL;DR: In this paper, various vortex generators were investigated under normal shock conditions with a diffuser at Mach number of 1.3, and it was found that a height of about half the boundary thickness and a large trailing edge gap yielded a fully attached flow downstream of the device.

91 citations

Journal ArticleDOI
TL;DR: In this article, the cross-stream inertial migration of neutrally buoyant deformable particles in a pressure-driven channel flow is studied using three-dimensional computer simulations, where the particles are modeled as elastic shells filled with a viscous fluid.
Abstract: Using three-dimensional computer simulations, we study the cross-stream inertial migration of neutrally buoyant deformable particles in a pressure-driven channel flow. The particles are modeled as elastic shells filled with a viscous fluid. We show that the particles equilibrate in a channel flow at off-center positions that depend on particle size, shell compliance, and the viscosity of encapsulated fluid. These equilibrium positions, however, are practically independent of the magnitude of channel Reynolds number in the range between 1 and 100. The results of our studies can be useful for sorting, focusing, and separation of micrometer-sized synthetic particles and biological cells.

91 citations

Journal ArticleDOI
01 Jan 2017-Energy
TL;DR: In this article, the aerodynamic performance of the airfoil S809 without and with vortex generators was investigated using a computational fluid dynamic method of simulation, and the results were obtained with three-dimensional incompressible Reynolds-averaged Navier-Stokes equations.

91 citations


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