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

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

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.

scholarly journals Hydraulic physical model production with Computer Numerically Controlled (CNC) manufacturing techniques

2018 ◽  
Vol 40 ◽  
pp. 05065 ◽  
Author(s):  
Pierre-Yves Henry ◽  
Jochen Aberle ◽  
Christy Ushanth Navaratnam ◽  
Nils Ruther
Keyword(s):  
Surface Roughness ◽  
Physical Models ◽  
Roughness Effects ◽  
Scaled Model ◽  
Construction Methods ◽  
Roughness Elements ◽  
Computer Numerically Controlled ◽  
Complex Boundary ◽  
Manufacturing Techniques ◽  
Scaled Models

Physical models are a well-accepted tool in hydraulic engineering, allowing for the detailed characterisation of flow processes and the validation of structure designs with complex boundary conditions. The methods used to construct physical models typically produce a surface roughness which does not necessarily scale with the surface roughness of the prototype. In this context, this paper discusses novel construction methods allowing a detailed reproduction of roughness elements in scaled models, such as Computer Numerically Controlled (CNC) manufacturing techniques and bed casting techniques. In particular, the present paper details the protocols developed to mill out a correct representation of the complex rock-fractured geometry of a closed channel which was obtained from Terrestrial Laser Scanners. The novelty of this scaled model production is the implementation of optical accesses in a closed (pressurized) hydraulic model, to allow for Particle Image Velocimetry measurements with a minimum impact on the reproduced roughness elements. The effectiveness of this production protocol is discussed in the context of modelling the roughness effects on the flow regime.

Coherent structures in direct numerical simulation of turbulent boundary layers at Mach 3

2007 ◽  
Vol 594 ◽  
pp. 59-69 ◽  
Author(s):  
MATTHEW J. RINGUETTE ◽  
MINWEI WU ◽  
M. PINO MARTÍN
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Boundary Layers ◽  
Coherent Structures ◽  
Mass Flux ◽  
Large Scale ◽  
Turbulent Boundary Layers ◽  
Turbulence Structure ◽  
Taylor’S Hypothesis ◽  
Mach 3

We demonstrate that data from direct numerical simulation of turbulent boundary layers at Mach 3 exhibit the same large-scale coherent structures that are found in supersonic and subsonic experiments, namely elongated, low-speed features in the logarithmic region and hairpin vortex packets. Contour plots of the streamwise mass flux show very long low-momentum structures in the logarithmic layer. These low-momentum features carry about one-third of the turbulent kinetic energy. Using Taylor's hypothesis, we find that these structures prevail and meander for very long streamwise distances. Structure lengths on the order of 100 boundary layer thicknesses are observed. Length scales obtained from correlations of the streamwise mass flux severely underpredict the extent of these structures, most likely because of their significant meandering in the spanwise direction. A hairpin-packet-finding algorithm is employed to determine the average packet properties, and we find that the Mach 3 packets are similar to those observed at subsonic conditions. A connection between the wall shear stress and hairpin packets is observed. Visualization of the instantaneous turbulence structure shows that groups of hairpin packets are frequently located above the long low-momentum structures. This finding is consistent with the very large-scale motion model of Kim & Adrian (1999).

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