Surface roughness effects on turbulent boundary layers on a flat plate located in an open channel / Effets de la rugosité de surface sur les couches limites turbulentes d'une plaque plane située dans un canal ouvert

2004 ◽  
Vol 42 (3) ◽  
pp. 247-261 ◽  
Author(s):  
Ram Balachandar ◽  
Deighen Blakely
Keyword(s):  
Surface Roughness ◽  
Flat Plate ◽  
Boundary Layers ◽  
Open Channel ◽  
Turbulent Boundary Layers ◽  
Roughness Effects

Roughness Effects on the Mixing Properties in Open Channel Turbulent Boundary Layers

2004 ◽  
Vol 126 (6) ◽  
pp. 1025-1032 ◽  
Author(s):  
Mark F. Tachie ◽  
Donald J. Bergstrom ◽  
Ram Balachandar
Keyword(s):  
Surface Roughness ◽  
Boundary Layers ◽  
Open Channel ◽  
Turbulent Boundary Layers ◽  
Turbulence Structure ◽  
Roughness Effects ◽  
Mixing Properties ◽  
Roughness Elements ◽  
Specific Geometry ◽  
Transport And Mixing

This paper investigates the effects of surface roughness on the transport and mixing properties in turbulent boundary layers created in an open channel. The measurements were obtained on a smooth and two different types of rough surfaces using a laser Doppler anemometer. The results show that surface roughness enhances the levels of the turbulence kinetic energy, turbulence production, and diffusion over most of the boundary layer. The distributions of the eddy viscosity and mixing length are also strongly modified by surface roughness. Furthermore, the extent to which surface roughness modifies the turbulence structure depends on the specific geometry of the roughness elements.

Surface roughness effects in turbulent boundary layers

1999 ◽  
Vol 27 (5) ◽  
pp. 450-460 ◽  
Author(s):  
P.-Å. Krogstadt ◽  
R.A. Antonia
Keyword(s):  
Surface Roughness ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Roughness Effects

A Study on Turbulent Boundary Layers on a Smooth Flat Plate in an Open Channel

2001 ◽  
Vol 123 (2) ◽  
pp. 394-400 ◽  
Author(s):  
Ram Balachandar ◽  
D. Blakely ◽  
M. Tachie ◽  
G. Putz
Keyword(s):  
Flat Plate ◽  
Froude Number ◽  
Boundary Layers ◽  
Open Channel ◽  
Reynolds Numbers ◽  
Turbulent Boundary Layers ◽  
Wall Region ◽  
Mean Velocity ◽  
Number Range ◽  
High Reynolds

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.

Theoretical Approach to Turbulent Lubrication Problems Including Surface Roughness Effects

1989 ◽  
Vol 111 (1) ◽  
pp. 17-22 ◽  
Author(s):  
H. Hashimoto ◽  
S. Wada
Keyword(s):  
Surface Roughness ◽  
Velocity Distribution ◽  
Boundary Layers ◽  
Theoretical Approach ◽  
Turbulent Boundary Layers ◽  
Distribution Law ◽  
Roughness Effects ◽  
Relative Roughness ◽  
Lubrication Equation ◽  
Lubrication Characteristics

A new theoretical approach to turbulent lubrication problems including the surface roughness effects is described. On the basis of a logarithmic velocity distribution law in the turbulent boundary layers, the resistance laws for pressure and shear flows in the lubricant film are formulated separately in both cases of smooth and homogeneous rough surfaces. Moreover, combining the bulk flow concept proposed by Hirs with the formulated resistance laws, the generalized turbulent lubrication equation including the surface roughness effects is derived. Some numerical results for the modified turbulence coefficients are presented in the graphic form for different values of relative roughness, and the effects of surface roughness on the turbulent lubrication characteristics are generally discussed.

Roughness effects in low- Re ? open-channel turbulent boundary layers

2003 ◽  
Vol 35 (4) ◽  
pp. 338-346 ◽  
Author(s):  
M. F. Tachie ◽  
D. J. Bergstrom ◽  
R. Balachandar
Keyword(s):  
Boundary Layers ◽  
Open Channel ◽  
Turbulent Boundary Layers ◽  
Roughness Effects

The Effect of Surface Roughness and Favorable Pressure Gradient on Turbulent Boundary Layers

2011 ◽  
Author(s):  
Ju Hyun Shin ◽  
Seung Jin Song
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Flat Plate ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Layer Growth ◽  
Rough Wall ◽  
Favorable Pressure Gradient

Rough wall turbulent boundary layers subjected to pressure gradient have engineering interest for many fluid machinery applications. A number of investigations have been made to understand surface roughness and pressure gradient effects on turbulent boundary layer characteristics, but separately. In this paper, turbulent boundary layers over a flat plate with surface roughness and favorable pressure gradient (FPG) are experimentally investigated. Boundary layers in different streamwise locations were measured using boundary layer type hot-wire anemometry. Rough wall zero pressure gradient (ZPG) turbulent boundary layers were also measured to compare the result from the investigation. The surface roughness was applied by attaching sandpapers on the flat plate. The magnitude of surface roughness is representative of land-based gas turbine compressor blade. Pressure gradient was adjusted using movable endwall of the test section. Results from the measurement show characteristics of the turbulent boundary layer growth affected by both surface roughness and favorable pressure gradient.

Measurements in adverse-pressure-gradient turbulent boundary layers with a step change in surface roughness

1975 ◽  
Vol 70 (3) ◽  
pp. 573-593 ◽  
Author(s):  
W. H. Schofield
Keyword(s):  
Surface Roughness ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Turbulent Boundary Layers ◽  
Step Change ◽  
Internal Layer ◽  
Mean Velocity ◽  
Law Of The Wall

The response of turbulent boundary layers to sudden changes in surface roughness under adverse-pressure-gradient conditions has been studied experimentally. The roughness used was in the ‘d’ type array of Perry, Schofield & Joubert (1969). Two cases of a rough-to-smooth change in surface roughness were considered in the same arbitrary adverse pressure gradient. The two cases differed in the distance of the surface discontinuity from the leading edge and gave two sets of flow conditions for the establishment and growth of the internal layer which develops downstream from a change in surface roughness. These conditions were in turn different from those in the zero-pressure-gradient experiments of Antonia & Luxton. The results suggest that the growth of the new internal layer depends solely on the new conditions at the wall and scales with the local roughness length of that wall. Mean velocity profiles in the region after the step change in roughness were accurately described by Coles’ law of the wall-law of the wake combination, which contrasts with the zero-pressure-gradient results of Antonia & Luxton. The skin-friction coefficient after the step change in roughness did not overshoot the equilibrium distribution but made a slow adjustment downstream of the step. Comparisons of mean profiles indicate that similar defect profile shapes are produced in layers with arbitrary adverse pressure gradients at positions where the values of Clauser's equilibrium parameter β (= δ*τ−10dp/dx) are similar, provided that the pressure-gradient history and local values of the pressure gradient are also similar.

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