Flow structures in zero pressure-gradient turbulent boundary layers at high Reynolds numbers

An experimental study was undertaken to investigate the characteristics of turbulent boundary layers developing on smooth flat plate in an open channel flow at moderately high Froude numbers (0.25<Fr<1.1) and low momentum thickness Reynolds numbers 800<Reθ<2900. The low range of Reynolds numbers and the high Froude number range make the study important, as most other studies of this type have been conducted at high Reynolds numbers and lower Froude numbers (∼0.1). Velocity measurements were carried out using a laser-Doppler anemometer equipped with a beam expansion device to enable measurements close to the wall region. The shear velocities were computed using the near-wall measurements in the viscous subregion. The variables of interest include the longitudinal mean velocity, the turbulence intensity, and the velocity skewness and flatness distributions across the boundary layer. The applicability of a constant Coles’ wake parameter (Π=0.55) to open channel flows has been discounted. The effect of the Froude number on the above parameters was also examined.

Download Full-text

Investigations of the Flow in Curved Ducts at Large Reynolds Numbers

Journal of Applied Mechanics ◽

10.1115/1.4009857 ◽

1948 ◽

Vol 15 (4) ◽

pp. 344-348

Author(s):

J. R. Weske

Keyword(s):

Reynolds Number ◽

Pressure Drop ◽

Boundary Layers ◽

Reynolds Numbers ◽

Equation Of Motion ◽

Radius Ratio ◽

High Reynolds Numbers ◽

Net Pressure ◽

High Reynolds ◽

Curved Ducts

Abstract It is found that the flow in curved ducts at high Reynolds numbers may be analyzed by methods adapted from the theory of boundary layers. Integration of the equation of motion of the “shedding layer” led to relations for the net pressure drop of curved ducts as a function of radius ratio and of Reynolds number.

Download Full-text

Rough-Wall Turbulent Boundary Layers

Applied Mechanics Reviews ◽

10.1115/1.3119492 ◽

1991 ◽

Vol 44 (1) ◽

pp. 1-25 ◽

Cited By ~ 794

Author(s):

M. R. Raupach ◽

R. A. Antonia ◽

S. Rajagopalan

Keyword(s):

Boundary Layers ◽

Strong Support ◽

Reynolds Numbers ◽

Viscous Sublayer ◽

Turbulent Boundary Layers ◽

Rough Wall ◽

Roughness Sublayer ◽

Turbulence Structure ◽

Wall Boundary ◽

High Reynolds

This review considers theoretical and experimental knowledge of rough-wall turbulent boundary layers, drawing from both laboratory and atmospheric data. The former apply mainly to the region above the roughness sublayer (in which the roughness has a direct dynamical influence) whereas the latter resolve the structure of the roughness sublayer in some detail. Topics considered include the drag properties of rough surfaces as functions of the roughness geometry, the mean and turbulent velocity fields above the roughness sublayer, the properties of the flow close to and within the roughness canopy, and the nature of the organized motion in rough-wall boundary layers. Overall, there is strong support for the hypothesis of wall similarity: At sufficiently high Reynolds numbers, rough-wall and smooth-wall boundary layers have the same turbulence structure above the roughness (or viscous) sublayer, scaling with height, boundary-layer thickness, and friction velocity.

Download Full-text

Approach to an asymptotic state for zero pressure gradient turbulent boundary layers

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2006.1948 ◽

2007 ◽

Vol 365 (1852) ◽

pp. 755-770 ◽

Cited By ~ 149

Author(s):

Hassan M Nagib ◽

Kapil A Chauhan ◽

Peter A Monkewitz

Keyword(s):

Experimental Data ◽

Pressure Gradient ◽

Skin Friction ◽

Boundary Layers ◽

Classical Theory ◽

Reynolds Numbers ◽

Turbulent Boundary Layers ◽

Careful Examination ◽

Mean Velocity ◽

Logarithmic Law

Flat plate turbulent boundary layers under zero pressure gradient at high Reynolds numbers are studied to reveal appropriate scale relations and asymptotic behaviour. Careful examination of the skin-friction coefficient results confirms the necessity for direct and independent measurement of wall shear stress. We find that many of the previously proposed empirical relations accurately describe the local C f behaviour when modified and underpinned by the same experimental data. The variation of the integral parameter, H , shows consistent agreement between the experimental data and the relation from classical theory. In accordance with the classical theory, the ratio of Δ and δ asymptotes to a constant. Then, the usefulness of the ratio of appropriately defined mean and turbulent time-scales to define and diagnose equilibrium flow is established. Next, the description of mean velocity profiles is revisited, and the validity of the logarithmic law is re-established using both the mean velocity profile and its diagnostic function. The wake parameter, Π , is shown to reach an asymptotic value at the highest available experimental Reynolds numbers if correct values of logarithmic-law constants and an appropriate skin-friction estimate are used. The paper closes with a discussion of the Reynolds number trends of the outer velocity defect which are important to establish a consistent similarity theory and appropriate scaling.

Download Full-text