Chapter 5. Separating Flow from Diffusion Using Velocity-compensated Diffusion Encoding

Predictions have been made for a variety of experimental three-dimensional boundary layer flows with a single finite difference method which was used with three different turbulent stress models: (i) an eddy viscosity model, (ii) the “Nash” model, and (iii) the “Bradshaw” model. For many purposes, even the simplest stress model (eddy viscosity) was adequate to predict the mean velocity field. On the other hand, the profile of shear stress direction was not correctly predicted in one case by any model tested. The high sensitivity of the predicted results to free stream pressure gradient in separating flow cases is demonstrated.

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A Topological Study of the Genesis of a Horseshoe Vortex in the Symmetry Plane Due to an Adverse Pressure Gradient

10.1115/imece2001/fed-24926 ◽

2001 ◽

Author(s):

Martijn A. van den Berg ◽

Michael M. J. Proot ◽

Peter G. Bakker

Keyword(s):

Pressure Gradient ◽

Bifurcation Theory ◽

Nonlinear Differential Equations ◽

Nonlinear Dynamical System ◽

Symmetry Plane ◽

Adverse Pressure Gradient ◽

Horseshoe Vortex ◽

Nonlinear Dynamical ◽

Separating Flow ◽

Flow Through

Abstract The present paper describes the genesis of a horseshoe vortex in the symmetry plane in front of a juncture. In contrast to a previous topological investigation, the presence of the obstacle is no longer physically modelled. Instead, the pressure gradient, induced by the obstacle, has been used to represent its influence. Consequently, the results of this investigation can be applied to any symmetrical flow above a flat plate. The genesis of the vortical structure is analysed by using the theory of nonlinear differential equations and the bifurcation theory. In particular, the genesis of a horseshoe vortex can be described by the unfolding of the degenerate singularity resulting from a Jordan Normal Form with three vanishing eigenvalues and one linear term which is related to the adverse pressure gradient. The examination of this nonlinear dynamical system reveals that a horseshoe vortex emanates from a non-separating flow through two subsequent saddle-node bifurcations in different directions and the transition of a node into a focus located in the flow field.

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The flow past a rapidly rotating circular cylinder

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1957.0157 ◽

1957 ◽

Vol 242 (1228) ◽

pp. 108-115 ◽

Cited By ~ 22

Keyword(s):

Boundary Layer ◽

Circular Cylinder ◽

Present Theory ◽

Stream Velocity ◽

Two Dimensional ◽

Rotating Circular Cylinder ◽

Flow Past ◽

Separating Flow ◽

Two Dimensional Flow ◽

Uniform Stream

This paper considers the two-dimensional flow past a circular cylinder immersed in a uniform stream, when the cylinder rotates about its axis so fast that separation in suppressed. The solution of the flow in the boundary layer on the cylinder is obtained in the form of a power series in the ratio of the stream velocity to the cylinder's peripheral velocity, and expressions are deduced for the value of the circulation and the torque on the cylinder. The terms calculated explicitly are sufficient to give reliable numerical values over the whole range of rotational speeds for which the postulate of non-separating flow is justifiable. The previously accepted theory, due to Prandtl, predicted that the circulation should not exceed a certain limit, while the present theory indicates that the circulation increases indefinitely with increase of rotaional speed. Strong arguments against the older theory are put forward, but the experimental evidence available is inconclusive.

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The Influence of Periodically Incoming Wakes on the Separating Flow in a Compressor Cascade

High Performance Computing in Science and Engineering '08 ◽

10.1007/978-3-540-88303-6_15 ◽

2009 ◽

pp. 205-215

Author(s):

Jan G. Wissink ◽

Wolfgang Rodi

Keyword(s):

Compressor Cascade ◽

Separating Flow

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Separating Flow: Small-Scale, Large-Scale, and Nonlinear Unsteady Effects

Boundary-Layer Separation ◽

10.1007/978-3-642-83000-6_19 ◽

1987 ◽

pp. 331-345 ◽

Cited By ~ 2

Author(s):

F. T. Smith

Keyword(s):

Large Scale ◽

Small Scale ◽

Separating Flow ◽

Unsteady Effects

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Remoras pick where they stick on blue whales

Journal of Experimental Biology ◽

10.1242/jeb.226654 ◽

2020 ◽

Vol 223 (20) ◽

pp. jeb226654

Author(s):

Brooke E. Flammang ◽

Simone Marras ◽

Erik J. Anderson ◽

Oriol Lehmkuhl ◽

Abhishek Mukherjee ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Drag Reduction ◽

Experimental Work ◽

Ecological Monitoring ◽

Video Recordings ◽

Venturi Effect ◽

Separating Flow ◽

Dynamics Analyses ◽

Blue Whales

ABSTRACTAnimal-borne video recordings from blue whales in the open ocean show that remoras preferentially adhere to specific regions on the surface of the whale. Using empirical and computational fluid dynamics analyses, we show that remora attachment was specific to regions of separating flow and wakes caused by surface features on the whale. Adhesion at these locations offers remoras drag reduction of up to 71–84% compared with the freestream. Remoras were observed to move freely along the surface of the whale using skimming and sliding behaviors. Skimming provided drag reduction as high as 50–72% at some locations for some remora sizes, but little to none was available in regions where few to no remoras were observed. Experimental work suggests that the Venturi effect may help remoras stay near the whale while skimming. Understanding the flow environment around a swimming blue whale will inform the placement of biosensor tags to increase attachment time for extended ecological monitoring.

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