Structure of high and low shear-stress events in a turbulent boundary layer

An experimental and analytical study of the separation of a turbulent boundary layer is reported. The turbulent boundary-layer separation model proposed by Sandborn & Kline (1961) is demonstrated to predict the experimental results. Two distinct turbulent separation regions, an intermittent and a steady separation, with correspondingly different velocity distributions are confirmed. The true zero wall shear stress turbulent separation point is determined by electronic means. The associated mean velocity profile is shown to belong to the same family of profiles as found for laminar separation. The velocity distribution at the point of reattachment of a turbulent boundary layer behind a step is also shown to belong to the laminar separation family.Prediction of the location of steady turbulent boundary-layer separation is made using the technique employed by Stratford (1959) for intermittent separation.

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Plaque and Shear Stress Distribution in Human Coronary Bifurcations: a Multi-Slice Computed Tomography Study

ASME 2007 Summer Bioengineering Conference ◽

10.1115/sbc2007-176309 ◽

2007 ◽

Cited By ~ 1

Author(s):

Alina G. van der Giessen ◽

Jolanda J. Wentzel ◽

Frans N. van de Vosse ◽

Antonius F. van der Steen ◽

Pim J. de Feyter ◽

...

Keyword(s):

Computed Tomography ◽

Shear Stress ◽

Outer Wall ◽

Atherosclerotic Plaques ◽

Advanced Stage ◽

Flow Divider ◽

Low Shear Stress ◽

Curved Vessels ◽

Early Atherosclerosis ◽

Low Shear

It is generally accepted that early atherosclerosis develops in low shear-stress (SS) regions such as the outer wall of arterial bifurcations and the inner bend of curved vessels (1). However, in clinical practice, it is common to observe atherosclerotic plaques at the flow-divider, or carina, of coronary bifurcations (2). Plaques at the carina are more frequently found in symptomatic patients, and may represent a more advanced stage of atherosclerosis. The carina is located in a region which is exposed to high SS. We hypothesize that if plaques are located in atheroprotective high SS regions, they have grown circumferentially from the atherogenic low SS regions.

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The accelerated fully rough turbulent boundary layer

Journal of Fluid Mechanics ◽

10.1017/s0022112077000810 ◽

1977 ◽

Vol 82 (3) ◽

pp. 507-528 ◽

Cited By ~ 31

Author(s):

Hugh W. Coleman ◽

Robert J. Moffat ◽

William M. Kays

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Turbulent Boundary Layer ◽

Pressure Gradient ◽

Stress Tensor ◽

Skin Friction ◽

Shape Factor ◽

Reynolds Shear Stress ◽

Smooth Wall ◽

Mean Velocity

The behaviour of a fully rough turbulent boundary layer subjected to favourable pressure gradients both with and without blowing was investigated experimentally using a porous test surface composed of densely packed spheres of uniform size. Measurements of profiles of mean velocity and the components of the Reynolds-stress tensor are reported for both unblown and blown layers. Skin-friction coefficients were determined from measurements of the Reynolds shear stress and mean velocity.An appropriate acceleration parameterKrfor fully rough layers is defined which is dependent on a characteristic roughness dimension but independent of molecular viscosity. For a constant blowing fractionFgreater than or equal to zero, the fully rough turbulent boundary layer reaches an equilibrium state whenKris held constant. Profiles of the mean velocity and the components of the Reynolds-stress tensor are then similar in the flow direction and the skin-friction coefficient, momentum thickness, boundary-layer shape factor and the Clauser shape factor and pressure-gradient parameter all become constant.Acceleration of a fully rough layer decreases the normalized turbulent kinetic energy and makes the turbulence field much less isotropic in the inner region (forFequal to zero) compared with zero-pressure-gradient fully rough layers. The values of the Reynolds-shear-stress correlation coefficients, however, are unaffected by acceleration or blowing and are identical with values previously reported for smooth-wall and zero-pressure-gradient rough-wall flows. Increasing values of the roughness Reynolds number with acceleration indicate that the fully rough layer does not tend towards the transitionally rough or smooth-wall state when accelerated.

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A Superposition Analysis of the Turbulent Boundary Layer in an Adverse Pressure Gradient

Journal of Applied Mechanics ◽

10.1115/1.4010226 ◽

1951 ◽

Vol 18 (1) ◽

pp. 95-100

Author(s):

Donald Ross ◽

J. M. Robertson

Keyword(s):

Boundary Layer ◽

Shear Stress ◽

Wall Shear Stress ◽

Turbulent Boundary Layer ◽

Velocity Profile ◽

Pressure Gradient ◽

Adverse Pressure Gradient ◽

Pressure Recovery ◽

Stress Coefficient ◽

Wall Shear

Abstract As an interim solution to the problem of the turbulent boundary layer in an adverse pressure gradient, a super-position method of analysis has been developed. In this method, the velocity profile is considered to be the result of two effects: the wall shear stress and the pressure recovery. These are superimposed, yielding an expression for the velocity profiles which approximate measured distributions. The theory also leads to a more reasonable expression for the wall shear-stress coefficient.

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