Discussion: “An Analytical Study of Separated Flow About Circular Cylinders” (Sarpkaya, T., 1968, ASME J. Basic Eng., 90, pp. 511–518)

1968 ◽  
Vol 90 (4) ◽  
pp. 518-519
Author(s):  
E. S. Tillman
Keyword(s):  
Analytical Study ◽  
Separated Flow ◽  
Circular Cylinders

An Analytical Study of Separated Flow About Circular Cylinders

1968 ◽  
Vol 90 (4) ◽  
pp. 511-518 ◽  
Author(s):  
T. Sarpkaya
Keyword(s):  
Analytical Study ◽  
Flow Model ◽  
Separated Flow ◽  
Shear Layers ◽  
The Body ◽  
Circular Cylinders ◽  
Vortex Sheets ◽  
Vortex Separation ◽  
Dependent Flow ◽  
Potential Flow Model

The forces acting on a circular cylinder by a time-dependent flow are analyzed through the use of a potential flow model. The shear layers which spring from the sides of the body are replaced by a combination of line vortices and infinite number of vortex sheets which connect the nascent vortices to their respective feeding zones. The analysis is then applied to the prediction of the kinematic and dynamic characteristics of symmetric vortex separation on circular cylinders. The results compare favorably with the latest available experimental data. The development of the wake is also traced and the results show the primary and secondary roll-ups of the shear layers as represented by the line vortices and vortex sheets.

Experiments on the stability of sinusoidal flow over a circular cylinder

2002 ◽  
Vol 457 ◽  
pp. 157-180 ◽  
Author(s):  
TURGUT SARPKAYA
Keyword(s):  
Stokes Flow ◽  
Coherent Structures ◽  
High Speed ◽  
Three Dimensional ◽  
Separated Flow ◽  
Circular Cylinders ◽  
Centrifugal Forces ◽  
Complex Interactions ◽  
Sinusoidal Flow ◽  
The Stability

The instabilities in a sinusoidally oscillating non-separated flow over smooth circular cylinders in the range of Keulegan–Carpenter numbers, K, from about 0.02 to 1 and Stokes numbers, β, from about 103 to 1.4 × 106 have been observed from inception to chaos using several high-speed imagers and laser-induced fluorescence. The instabilities ranged from small quasi-coherent structures, as in Stokes flow over a flat wall (Sarpkaya 1993), to three-dimensional spanwise perturbations because of the centrifugal forces induced by the curvature of the boundary layer (Taylor–Görtler instability). These gave rise to streamwise-oriented counter-rotating vortices or mushroom-shaped coherent structures as K approached the Kh values theoretically predicted by Hall (1984). Further increases in K for a given β led first to complex interactions between the coherent structures and then to chaotic motion. The mapping of the observations led to the delineation of four states of flow in the (K, β)-plane: stable, marginal, unstable, and chaotic.

scholarly journals On analytical study of factional Oldroyd-B flow in annular region of two torsionally oscillating cylinders

2012 ◽  
Vol 16 (2) ◽  
pp. 411-421 ◽  
Author(s):  
A. Mahmood
Keyword(s):  
Shear Stress ◽  
Velocity Field ◽  
Analytical Study ◽  
Analytic Solutions ◽  
Circular Cylinders ◽  
Second Grade ◽  
General Solutions ◽  
Exact Analytic Solutions ◽  
Governing Differential Equation ◽  
R Functions

The velocity field and the associated shear stress corresponding to the torsional oscillatory flow of a fractional Oldroyd-B fluid, also called generalized Oldroyd-B fluid (GOF), between two infinite coaxial circular cylinders, are determined by means of the Laplace and Hankel transforms. Initially, the fluid and cylinders are at rest and after some time both cylinders suddenly begin to oscillate around their common axis with different angular frequencies of their velocities. The exact analytic solutions of the velocity field and associated shear stress, that have been obtained, are presented under integral and series forms in terms of generalized G and R functions. Moreover, these solutions satisfy the governing differential equation and all imposed initial and boundary conditions. The respective solutions for the motion between the cylinders, when one of them is at rest, can be obtained from our general solutions. Furthermore, the corresponding solutions for the similar flow of classical Oldroyd-B, generalized Maxwell, classical Maxwell, generalized second grade, classical second grade and Newtonian fluids are also obtained as limiting cases of our general solutions.

Velocity spikes in separated flows

1966 ◽  
Vol 25 (1) ◽  
pp. 43-50 ◽  
Author(s):  
F. B. Hanson ◽  
S. H. Kozak ◽  
P. D. Richardson
Keyword(s):  
Large Scale ◽  
Separated Flow ◽  
Circular Cylinders ◽  
Hot Wire ◽  
Separated Shear Layer ◽  
Von Karman ◽  
Air Stream ◽  
Close Proximity ◽  
Karman Street ◽  
Von Kármán

In a recent study related to transition in the wake flows behind circular cylinders held transversely to an air stream, Bloor (1964) has reported the observation of velocity ‘spikes’ and attributed these to the close proximity to the hot wire of vortex centres on the opposite side of the von Kármán vortex street. Further observations of spikes are reported here, and the characteristics of their distribution indicate that other explanations of their form must be found. Some idealized flows are considered, and it is concluded that observations of spikiness within the hot-wire output may be accountable in terms of large-scale distributions of vorticity within the flow convected past the wire, the distributions being reasonable representations of a separated flow. The observations also provide some evidence that small vortices of Strouhal frequency exist on the inside of the coherent separated shear layer, and this may assist in the understanding of the feed-back mechanism where by the von Kármán street establishes itself as a self-perpetuating phenomenon.

Heat Transfer in Turbulent Boundary-Layer Separation Over a Surface Cavity

1967 ◽  
Vol 89 (4) ◽  
pp. 335-340 ◽  
Author(s):  
R. L. Haugen ◽  
A. M. Dhanak
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Analytical Study ◽  
Separated Flow ◽  
Boundary Layer Separation ◽  
Eddy Diffusion ◽  
Uniform Heat Flux ◽  
Surface Cavity ◽  
Good Agreement

An experimental and analytical study is presented in this paper describing heat transfer in the region of separated flow over a two-dimensional rectangular cavity (of variable depth-width ratios) facing an oncoming turbulent boundary layer of variable thickness. The analysis, based on a prescription of eddy diffusion in the mixing region, predicts a heat transfer correlation, in terms of the foregoing variables, resulting in good agreement with the data. Experiments were performed with conditions of uniform temperature and uniform heat flux at the cavity walls and revealed no substantial difference between the two methods on the final correlation.

3D-Flow Structures Behind Truncated Circular Cylinders

2003 ◽  
Author(s):  
Alfred Leder
Keyword(s):  
Experimental Investigation ◽  
Flow Characteristics ◽  
Separated Flow ◽  
Laser Doppler Anemometer ◽  
Circular Cylinders ◽  
Flow Structures ◽  
3D Flow ◽  
Vortical Flows ◽  
Turbulence Structures ◽  
Recirculating Flow

An experimental investigation of the two flows around finite circular cylinders with different head geometries mounted on a flat plate, see fig. 1, is reported. The aspect ratio L/D (with length L and diameter D) of both cylinder models is 2.0. The focus of this study is toward examining the complex separated flow structures and wake properties as well as the influence of the head geometry on the flow characteristics. Velocity and turbulence measurements have been carried out with a three component Laser Doppler anemometer (LDA) at the Reynolds number ReD = 2.0 · 105. The experimental results show complex 3D fluid motions in the regions of separated flow. They are induced by the superposition of three main vortical flows. The developing vortex and turbulence structures for both investigated models show similar overall features. Differences in the geometries of the 3D-envelopes of the recirculating flow as well as in the distributions of turbulent terms can be allocated to differences in the vortical flows over the free end surfaces of the cylinders.

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